Is Big Sur stable enough to install on iMac 2019?

Big Sur will still be there when you get ready to install it. Please bear with me as I share some things to consider. Most of the problems people have encountered after installing an upgrade are not due to the Apple OS. What often happens is one of two things. Either when the problem, or problems, are finally resolved, it turns out to be due to something else, not Apple's operating system. When we install an OS upgrade like Big Sur, it often seems to uncover underlying existing issues for various reasons. Sometimes there is an app which causes problems such an antivirus app or a Mac cleaning app. Or there may be some conflicting extensions, etc. Sometimes the problem is due to doing a download via Wi-Fi. Oftentimes the file will get corrupted and either not finish downloading or will not install. If it does install, they may be serious problems with the computer because of the corruption. Such downloads should only be done via a wired Ethernet connection to ensure a safe installation. So, in summary, the problems encountered are due to corruption or conflicts, not normally due to the upgrade. I have used the Big Sur beta and the regular installation for months now, and it has performed as it should. I hope you find the information useful.

Thank you for the kind words. If, after the upgrade, you do encounter any problems, let us know. That is why there are some very experienced people here with solutions at the ready.

For most people it is working just fine. As always, do not upgrade without a solid backup in place.