It's weird. My post disappeared. Do moderators want to hear only positive reviews? Ok, let me try it again.
Upgrade was done with easy with Opencore 0.7.4. But I experienced many issues. Monterey's Finder got stalled when I tried to access the SMB network drive. The only way to escape from the situation was rebooting. I could workaround the issue by changing the server's SMB settings, but macOS shouldn't have been halted by meer network drive access.
The other issue with Monterey is software incompatibility. Photoshop 2018 and Acrobat Pro 2018 didn't work with Monterey. Some of system libraries that the software was linked to are removed in the Monterey. Someone may say it's not Monterey's fault but your problem or adobe's fault. Well, I don't think so as the system libraries did exist in Big Sur but removed in Monterey. I guess Apple have removed them while improving M1 support.
I got a bluetooth issue but it could be solved by
https://dortania.github.io/OpenCore-Install-Guide/extras/monterey.html#bluetooth.