I have a 12th gen Intel Framework running Arch. I love it, although as others have pointed out the battery life could be better. Early kernels shortly after release had some incompatibility issues that required specific kernel arguments to fix. Also I had to blacklist the light sensor as it conflicted with the brightness function keys.
The Arch wiki has a page with details on Framework laptops you may appreciate looking at.
That's hard for me to answer because I'm usually at home plugged in, and I set the max charge in the bios to only 65% so the battery will physically degrade slower (I don't need the charge). A few hours is really all I can say with any accuracy. Worth noting a few things -
I will say that if long battery life is your #1 concern this may not be the laptop for you.