8GB RAM is adequate, but 16-24GB would be better. I'm running Monterey flawlessly on 20GB (2018 Mac mini) but so far haven't ever actually needed more than 16GB.
Three OS versions you should consider:
a) Mojave (10.14) - Last version with 32-bit app support. If you are still on Sierra you might have legacy applications that are still important... or not.
b) Big Sur (11) - I usually consider the penultimate supported OS to provide optimal performance.
c) Monterey (12) - Slightly more resource intensive than Big Sur which can be noticeable on older hardware (16GB+ RAM recommended), but it is also the oldest that supports Apple iWork (Pages, Numbers, etc) updates so installing this will offer better modern software support.
Big Sur and Monterey also prefer to run on SSDs. If you have a 1TB Fusion drive and wish to run Big Sur or newer I would suggest buying a high capacity external USB 3.0 SSD and installing MacOS onto that.