I'd start by going to Samsung Members app > Get Help
& Diagnostics & check the battery there.
Depending on the result of the battery test, you'll have a better idea, if it's a dying battery, or if you have apps that are running excessively in the background.
From phone being off
Hold power and volume up until the phone vibrates and a android guy appears
Then press volume down to clear cache then power button to select.
See if that helps.
But you only got a 3100 mah battery. You're on par with the S9. With constant use I only got about 3.5 hrs.
You can do some things like turn off bluetooth. If constantly searching it will drain. Also turn off adaptive display and manually set brightness.
the s9 has a bigger screen and it's older with a slightly smaller battery. so that makes sense being 3 years and a half since release date