How do I fix screen flickering, app closing, and random writing on iPhone Pro Max with iOS 16.5.1?

If it has a non-Apple screen that is the prime suspect.

Beyond that:

• Your battery needs to be replaced→iPhone Battery Replacement - Official Apple Support
• The current iOS version is 18.4.1, and you should upgrade to it
• 600 is far to many tabs-each uses a fixed piece of RAM so everything else (those 116 apps) must be constantly swapped in and out, which will significantly slow down your iphone
• 430 GB out of what?
• The amount of iCloud storage is irrelevant; it does not add any storage to your phone, it is for syncing and backup.

OK, so.......the things which are likely causing issues:

1. Your battery should have been replaced a while ago. When Battery health dips to 80% or less, its useful life has been spent.
2. The fact an non-authentic screen was put on your iPhone, means Apple won't replace the battery in the phone as they won't touch a phone which has been tampered with, with non-authentic parts
3. The amount of storage you have in iCloud has NOTHING to do with how much storage is on your phone. Unless your phone is 1TB, you've used a significant amount of storage on the phone itself, which can cause all sorts of issues.
4. If it were me, I'd buy a new iPhone at this point.

Do you think Apple will even consider replacing the battery in a phone which has been tampered with?