14 Pro extremely laggy after iOS 26.2 upgrade

Have you tried a forced restart:

1. Press and quickly release the volume up button.
2. Press and quickly release the volume down button.
3. Press and hold the side button until you see the Apple logo (this might take longer than 10 seconds).

The operative word here is QUICKLY for the first two buttons, then a long hold for the SIDE button; and try it a couple of times, the timing is a little tricky. If done correctly this will always work unless the phone has a hardware problem. 

Also, do you have a 3rd party VPN installed, even if you are not using it? If so, delete the VPN profile in Settings/General/VPN & Device Management/VPN, then restart your device. Don't just turn it off; delete the profile. Updates sometimes need to have VPN to be removed and reinstalled. If that fixes it, you can try reinstalling VPN, but probably shouldn't.

xb4it wrote:

it started horribly lagging, like I was using 15 year old Android device

There may be several reasons due to which an iPhone may behave as described by you. Some of them could be...

Let's delve a bit deeper into some of them:

1. Storage: A full iPhone can definitely slow things down. Phones can experience performance issues when the storage is nearly full. Users can check their storage status by going to Settings > General > [Device] Storage. Deleting unnecessary apps, photos, or videos can free up space and improve performance. How to check the storage on your iPhone and iPad - Apple Support.
2. Battery Health: A degraded battery can impact performance. A deteriorating battery can impact the overall performance of an iPhone. Checking the battery health can be done by going to Settings > Battery > Battery Health. If the maximum capacity is significantly reduced, it might be time to replace the battery. Prolong and Maximise Battery Performance … - Apple Community
3. Incorrect Handling: Accidental drops or bumps can cause internal damage. looking at the Apple's guide on proper handling is a good step. Important handling information for iPhone - Apple Support (IN)
4. Environmental Issues: Extreme temperatures, dust, and water exposure can all be detrimental.
   1. Keeping iPhone clean is an important step. Dust accumulation in the iPhone's ports and openings can affect functionality. Apple provides guidelines on how to clean iPhones safely, which usually involves using a soft, lint-free cloth to remove dust without causing damage. Cleaning your iPhone - Apple Support
   2. Keep the iPhone within temperature limits. Phones are designed to operate within a specific temperature range. Exposure to extreme temperatures, especially in parked cars, can lead to overheating or other performance issues. If your iPhone or iPad gets too hot or too cold - Apple Support.
   3. Addressing safety issues is also important: Important safety information for iPhone - Apple Support (IN)
5. Unauthorized Service: Servicing an iPhone through unauthorized channels can result in substandard repairs and void warranties. Users should always seek authorized Apple service centers for repairs and maintenance.
   1. Repairs by unqualified technicians can introduce new problems. Find information about your warranty or AppleCare plan - Apple Support is helpful.
   2. Modification / Alteration of an iPhone by a third-party vendor may cause issues beyond repair. --> Unauthorized modification of iOS - Apple Support (IN)
6. Jailbreak: Now, let's talk about jailbreaking. Jailbreaking removes Apple's restrictions, allowing for more customization and app installation outside the App Store. However, it can also lead to instability, security vulnerabilities, and issues receiving future iOS updates.

By considering all these possibilities, you've provided a comprehensive approach to troubleshooting the iPhone's behavior.

Understanding and addressing these factors can help you maintain the optimal performance and longevity of their iPhones. Following Apple's guidelines and seeking authorized support when needed are crucial for a positive user experience.

If you are sure it is the fault of the equipment.

If you have either dropped the device accidentally or exposed it to liquid or used it beyond acceptable temperature limits then…

Take your device to an Apple Retail Store or Apple Authorized Service Provider, or contact Apple Support:

Find Locations - Location Selector - Apple

Contact Apple for support and service - Apple Support 

Get a Genius Bar Reservation and Apple Support Options - Apple

Contact Genius Bar.

Manage Reservations - My Reservations - Apple

Lagging issues are not always the iOS update's fault!  Many things can cause phone problems.  If you tell people you think it's an iOS update, it might make it harder to fix or find a solution for the real issue.

Remember, the right question often leads to the solution!

Was/Is your device Jailbroken? If that's the situation, please be informed that attributing the issues to iOS updates may not be accurate.

iOS updates aim to enhance user experience, boost security, and fix bugs rather than disrupt core features. The majority of the issues after updates might stem from underlying, unmentioned factors. Updates won't typically alter personal data but may refine settings or features. Backup before major updates for safety. Review Apple's update details and backup advice for a smooth process.

Kindly consider checking your settings and addressing any device issues before attributing the issue to external factors. This could be a pure coincidence that the iOS update affected the iPhone functions.

Before initiating a standard iOS update, it's advisable to create a backup. Have you completed this step? If yes, proceed with the restoration from the backup.

See what each update does: OS — iOS 26, About iOS 18 Updates, About iOS 17 Updates, About iOS 16 Updates, About iOS 15 Updates, About iOS 14 Updates, About iOS 13 Updates, About iOS 12 Updates, and so on...

The term used by you, "Immediately after the update," is purely coincidental, and it surely is not iOS 26.2 because...

I conducted a thorough search of this forum using the term 'Lag after iOS' and uncovered numerous posts detailing similar issues across various iOS updates. This suggests that iOS updates may not consistently be the root cause. Below are a handful of examples extracted from the search results:

Re: iPhone started to lag after updating to iOS 15.8.1.

why did my phone lagged after updating in ios 16

Re: My iPhone 13 Pro Max is running slow after updating to iOS 17.5.1

12 pro max lagging after updating to ios 17

why is my 16 pro max slow after 18.3.1 update

Iphone 14 pro lagging after ios16.6 update

iPad lag after updating iPadOS 15.5.1

iPhone is slow after updating to iOS 17.03

Re: My phones lagging after update 14.0.1

iPhone 12 Pro running slow after iOS 15 update

iPhone 7 is very slow after 11.2 update

iPhone 5c slow and lags after updating to IOS 9

iphone 6 plus has become very slow after updating it to ios 10.3.1

Reports of device lag appear across all models and iOS versions in this forum, suggesting the issue is device-specific rather than tied to any particular iOS version or model.

Handling. Handle your iPhone with care. · Repairing. iPhone should only be serviced by a trained technician. · Battery. · Lasers. · Distraction. · Navigation. · Charging.Cleaning.

Important safety information for iPhone

Clean iPhone immediately if it comes in contact with anything that may cause stains, or other damage—for example, dirt or sand, ink, makeup, soap

Important handling information for iPhone

I have iOS 26.2 on iPhone 13XR.

I feel it’s a marginal update at best. I could key in entire paragraphs easily before; now it adds words without my permission. This and problems with Preview are things I dislike most.

"14 Pro extremely laggy after iOS 26.2 upgrade: I've been using iPhone 14 Pro since it came out, and had 0 issues whatsover. Today I decided to update the OS to iOS 26.2 (23C55) and I have to say it's just completely unusable.: [...]Why did they even try to change the OS design, which was already close to perfection - no clue, nonetheless is there any workaround that might help with this issue?"

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Using a New UI:

Likely from feedback from consumers --many, if not most, of which are provided directly on Apple's iPhone Feedback site: Feedback - iPhone - Apple. The Liquid Glass got so much primitive backlash, that they made it a fix in a short manor of time. If you didn't upgrade to iOS26 right when it was released, then, you wouldn't have gone though using such and unappealing and hard-to-use interface, like many of us did. Apple's decisions for this lopsided, and various participants on these forums yacked about it, but never provided feedback. Point Being: User Interface changes are all about customer satisfaction; but that is not without its downsides (i.e. being non-user friendly).