"Power on AC attach" not working for Intel 12th gen in standalone mode

how can I check the version from the BIOS itself?

You can press F2 during boot and go into the setup menu. It’ll show your BIOS version there. Its should be 3.0X something. The latest version is 3.08
See here: Framework Laptop BIOS and Driver Releases (12th Gen Intel® Core™)

Have you got the coincell battery installed?