For me macOS 12 Monterey was more stable than macOS 11 Big Sur.
see > Update macOS on Mac - Apple Support
If you're iMac is currently having any issues or low on disk space, then you need to fix those before upgrading.
If you need help looking for and sorting out problems.
Download and run the free version of EtreCheckPro, from > https://etrecheck.com/en/index.html
Then post your Report, as per > How to use the Add Text Feature When Post… - Apple Community
EDIT: I started to post to this in the iMac forum and it took me 10 minutes to be able to post after it was moved here....