You can revert this if you unlock your bootloader:

https://xdaforums.com/t/undo-the-january-2025-update-without...

(EDIT: Just to be clear, and which is also mentioned in that post: unlocking the bootloader will reset the device. If your device is already unlocked though, you will be able to keep the data.)

Of course, I would just advise to switch to LineageOS directly, since Google has stopped providing security updates for the Pixel 4a already in August 2023. I've run LineageOS for years on the Pixel 4a and it has worked pretty much perfectly for me:

https://wiki.lineageos.org/devices/sunfish/

Android 15 (LineageOS 22) was just released for it.