After IOS 18.0.1 update my iPhone’s speakers have a low volume

It's 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! Please look in the right direction.

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: 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...

Apple software releases for the past few years are seldom optimized to work on older devices. I had my iPhone 13 PM go through a display replacement because of Green screen issue after software updates. For that matter, even iPhone 16 series was launched with various software bugs in iOS 18 for which Apple had to release fixes through iOS 18.0.1, Apple themselves have acknowledged this and you can also the check the change log of iOS 18.0.1 release.

So to summarize, the problem lies with the tunning of software to suit the hardware of the model. For eg., Windows 11 can't run on older PC's but if you force install it by other means, your graphics card might burn out or motherboard might not work or display might fail or any other hardware related problems might occur. Now to say that it's not the software compatibility issue in why view is a absurd argument.

Anyways, what is the hype all about?, the AI features?, think about this - anyways model till iPhone 15 plus aren't going to get them, but a Google tensor processor or an basic 4nm based Snapdragon processor will have those by default. Think about all of this !!!

Finally, do a google search about the stability of OS before upgrading.

In addition to my previous reply, one more example is

OnePlus 12r will not get the same software update as OnePlus 12 does, or Samsung S23 might not be able to run the same update rolled out for Samsung S24 Ultra.