You may want to check if it has a "fusion drive" (hdd with small ssd cache), or an ssd.

IIRC, old macs with hard drives used non standard temperature sensors on the hard drives (instead of on cpu/gpu). When not running MacOS, the computer hardware couldn't tell what the temperature was, so it would run the fans at full speed just to be safe. It could get quite loud.

You might want to do some research on that particular model to see if it would be affected.

I could only find a single reddit thread about an iMac 2017. Everything works except internal sound.

Do try to install Linux and report back here and upload your results to linux-hardware.org They already have results for some iMac models and most seem to work quite well.

Why Linux on that machine? Why not BSD or OpenDarwin?