Lots of things happen in standby if you don't tweak your settings or even the web page you have it pointed to.
Here are some power saving settings I utilize when pushing its limits.
Disable majority of app notifications, except a few delivery quietly such as mail.
Announce notifications off,
Siri suggestions, do you need any? Otherwise turn them all off.
In Siri & Search I only have Show App in search active, everything else is off
No sound for new mail
Turn off bluetooth if not using
Auto Lock 2 mins
Display & Brightness use dark mode only
Good to monitor what apps are consuming most of battery, sometime you will see apps that are updating or doing something in the background that can consume power excessively.
FaceTime is a real battery consumer, use it sparingly if your worried bout battery life, or do it mostly with power is connected.
Don't leave your Safari with MacRumors foremost, as its rotating ads consume battery faster then 99% of web sites out there even in private mode even when you are not using safari. Even on my M1 iMac it complains their URL is consuming too much resources.
Pay attention to attention to screen brightness the higher it is exponentially faster your battery charge will go.
iCloud sync can waste battery too if syncing in the background.
Yes once you get the iPad mini 6 not doing so much in the background, don't have safari pointed to Mac Rumors, you get many hours from it after it is past its initial battery recharging period.