I bought an Iphone SE in January 2021. The battery performance was already rather poor - lasting less than a day with fairly light use.
I've purposely not upgraded IOS because I do not want to pull even less use time from the battery. But now my hand is being forced due to App Store needing the latest IOS to install new apps or update my current apps.
Given that some of my most used apps (eg Signal) require being up to date to open them, I appear to be left with the choice of either bricking the phone or running it at a highly reduced battery. Yes, I can text and make calls, but I could have bought a Nokia burner for that.
Also going to throw this out there (and I'm preparing for the commentary "you're saying don't use it herr derr") - are you on it a lot? I've observed my teens usage patterns and sometimes they are habitually just pulling the phone out and looking at the lock screen. This happens multiple times in minutes and the on/off of the screen is going to burn battery faster with no real usage. You may also have apps running in the background that use wifi/cellular, and that will drain the battery faster too. If you changed those settings to only use the network when the app is open then it will use less battery. Yeah you won't get updates when you aren't looking at those apps but, is that such a crucial thing?
You can take the phone somewhere and have them replace the battery for far much less than the cost of a new phone.