Sero_ wrote: "...the battery percentage is 88%. And two years have passed..."
Is that 88% the Maximum Capacity or simply the current charge? ...If it's the Max Capacity, it's well above Apple's 80% level for replacing the battery.
On the other hand, two years is when batteries can begin to weaken and struggle to meet the demands of videos, high frame rate games, etc.
Apple's iPhone User Guide says: "If your iPhone isn’t working as expected, you can try restarting it by turning it off, then turning it back on. If turning it off and on doesn’t fix the issue, try forcing it to restart.":
Turn iPhone on or off - Apple Support
...But if that doesn't help, consider replacing the battery:
iPhone Battery Service
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