Equal2024 does that mean that after 3 years, they stop offering a new major version of Android?
Thats all they are guaranteeing theyll offer, yes.
bowpay since Android 12 I've noticed severe battery drain issues on my Pixel 4a
I dont think its likely connected to the Android version you use.
Its much more likely that this is related to the apps you use or the way you use them/have them set up (e.g. Element can cause big battery drain for some people). Can try and disable individual apps. See if you notice much difference. Maybe uninstall and set them up again in case youve changed settings that impact battery drain.
Also possibly a change in the quality of your mobile network connection. A poor connection can have a big impact. More so if you are running certain apps (e.g. Signal without Google Play Services can cause much heavier drain in this condition)