Problems after update iOS 16.3

As this is not a known problem the only fix is the standard procedures below

Pre-repair procedure.

First thing I advise is to try a Forced restart

Force restart iPhone – Apple Support (UK)

If no better you could Backup, restore to factory, then restore from the backup:-

If necessary set up without restoring backup and test at that point, erase again, then restore from the backup:-

(If the phone needs attention you will have to do this anyway)

If you can import your media to Photos or iTunes in a computer and copy important documents to a cloud server it will give you some resilience in case the restore from backup fails, or you need to ditch the backup and start as new.

See here for the resources you need. Allow a couple of hours:

How to back up your iPhone, iPad, and iPod touch - Apple Support

Restore your iPhone, iPad, or iPod to factory settings - Apple Support

Restore your iPhone, iPad, or iPod touch from a backup - Apple Support

Otherwise arrange a repair for hardware failure

Click here > iPhone Repair & Service - Apple Support

Or

Click here > Contact - Official Apple Support

Anything other than Screen or Battery may be a replacement phone and the price is in the article under "Other damage"

See also: Get your iPhone, iPad, or iPod touch ready for service - Apple Support

Additional info on Face ID particularly with iphone X

Your Face ID True Depth camera may have failed, especially if you have the warning message. 

Using diagnostics available in iOS 14.6 or later, Apple has detected an issue with your True Depth camera that might cause it to not function as expected. The True Depth camera contains lasers, which might be disabled for safety reasons if the device malfunctions or is damaged. This won't prevent you from using your iPhone or iPad, but until your iPhone or iPad is updated or serviced, you might not be able to use Face ID, Animoji, Memoji, and some other features that use the front camera. 

If you get that message and can't enroll your face or unlock your device with Face ID, you can take your device to an Apple Store or Apple Authorized Service Provider, or contact Apple Support about your iPhone or your iPad.  

Click here >  Apple Support 

If you had the screen replaced other than by Apple it will never work again 

iPhone parts and service history – Apple Support (UK) 

About genuine iPhone displays – Apple Support (UK) 

See also Knowledge Base article If Face ID isn't working on your iPhone or iPad Pro - Apple Support 

First thing I advise is to try a Forced restart

Force restart iPhone – Apple Support (UK)

If no better you could Backup, restore to factory, then restore from the backup:-

If necessary set up without restoring backup and test at that point, erase again, then restore from the backup:-

(If the phone needs attention you will have to do this anyway)

If you can import your media to Photos or iTunes in a computer and copy important documents to a cloud server it will give you some resilience in case the restore from backup fails, or you need to ditch the backup and start as new.

See here for the resources you need. Allow a couple of hours:

How to back up your iPhone, iPad, and iPod touch - Apple Support

Restore your iPhone, iPad, or iPod to factory settings - Apple Support

Restore your iPhone, iPad, or iPod touch from a backup - Apple Support

Otherwise arrange a repair for hardware failure

Click here > iPhone Repair & Service - Apple Support

Or Click here > Contact - Official Apple Support

Anything other than Screen or Battery may be a replacement phone and the price is in the article under "Other damage"

See also: Get your iPhone, iPad, or iPod touch ready for service - Apple Support

I asked why you think Watch should not have your contacts in if you didn't unpair or erase it

Try this

Put your watch on its charger and keep it there until you complete these steps. (select the watch OS version) 

Erase Apple Watch – Apple Support (UK)

Erasing all content and settings this way erases all media, data, and settings from your Apple Watch, but it does not remove Activation Lock if it has one.

Or you can erase  and remove it from your account in Find My or https://icloud.com/find .

Wait for the process to finish, then set up your Apple Watch again. Set up your Apple Watch – Apple Support (UK)

When asked, decide to restore from a backup or set up as new.. 

I gave MY answers. I am not from Apple and quite frankly I have offered all I am prepared to offer.

If you have owned iphones for that long and never had to backup and restore then you have lived a charmed life so far.

If you do not want go through standard DIY remedies, check if the battery health is 80+% as Alancito suggested then arrange a repair.

Apple Watch Service & Repair - Apple Support

iPhone Repair & Service - Apple Support

I have another problem that has arisen since 16.3…I cannot open my Phone app! No recent calls list, keypad to dial numbers, just a black screen🤷🏽‍♂️ I’ve tried Reset, and a Hard Rest as described above.

I have owned iPhones since the first generation. I don’t understand how backing everything up to iCloud and resetting my iPhone will stop this. It’s kind of a huge deal for me to accomplish those steps. And, frankly, I’m not willing to do something that drastic that would take me hours to accomplish when I haven’t seen a single person on this forum say it works. Just by deduction, I’m gonna say this is APPLEs standard reply for bugs they can’t fix. “How about you do all this work we’re not sure actually helps.”

Buddhagod wrote: "...It really is ever 30 minutes …freeze, restart…and it takes like 10 minutes"

Buddhagod ~ That can be the behaviour of a weak battery — Does your iPhone still have its original battery?

And what's the Maximum Capacity % here?...

Settings > Battery > Battery Health & Charging

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I’m using my daughter’s iPhone to post this because I have the same issue after updating to IOS 16.3: I have a completely black screen. I cannot use my iPhone at all. No drops, no water damage; the only thing I did was the software update. The phone is charged. I think even the Apple Support doesn’t know about this. Anyone else have a black screen? I don’t want to do a factory or hard reset because I will lose my saved Alarms, and I need that. (I don’t use the Reminders because it *****; Alarms work best for me.).

My battery is fine, 84% capacity.

my memory is fine, 60+ GB available

ive done an update from recovery mode to reinstall the iOs

im very tech savvy, I’m just holding out that Apple will acknowledge the issue and fix it with an update so I don’t lose my data.

it’s crazy inconvenient though

Did you try https://discussions.apple.com/thread/254590771?answerId=258574980022#258574980022

Ever since updating my iPhone X to 16.3 my Bluetooth keeps dropping and Face ID does not work. I have switched off the phone and has not sorted the problem. Is there a fix for this

Yes, see my post above yours.

bluetooth connectivity messed up too

I’ve just realised that my Contact list is still visible on my iWatch!🤔🤷🏽‍♂️…I’ve looked, but cannot see any settings for this!?