After updating to ios 16.5, the incoming calls ringtone is very quiet

If the issues you mentioned are indeed caused by iOS, it's likely that numerous users who have upgraded to iOS 16.5 are experiencing similar problems.

With the limited information that you have provided, It is hard to even guess the problems faced by you. 

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Please re-post with detail so that someone else can help.

Happens to me too, I have iPhone mini 12, IOS 16.6.1 (Sept 2023 update). Apple does it on purpose, makes it difficult for you hoping you give up and throw out your phone. A smart way of forcing you to upgrade to a newer iPhone and throw out your old, really... They have done many updates over the years and I have thrown out several iPads because of Apple don't want to support previous hardware versions. They want to generate a throw-out-society, make people buy a new device every year is what they prefer. Watch out, they don't understand circular economy and are running campaigns to tell how good they are when reality tells a different story. Not a sustainable company in my view.

I have iPhone 8 and also facing same ring tone problem

Same issue with new iPhone 13. Anyone know a fix?