Hello nicholas_k0130,
We understand that the battery percentage on your iPhone will not change from 100% even while the phone has been in use for hours at a time. We also see that Low Power Mode still shows as active even though you have disabled it.
Since your device is already fully updated, let's see if we can get some info about your battery condition. Go to Settings > Battery. From there, tap on Battery Health.
What is the Maximum Capacity that is listed? Is it at or below 80%? What does it say under "Peak Performance Capability"? Do you see any alerts or messages regarding the battery condition or the performance?
If you do, or if the battery health shows 80% or less, then a battery replacement is recommended. This has more info.
If your Battery Health appears normal, and you have no alerts, then please reach out to Apple Support: Get Support
Take care.