Universal Control was announced at WWDC 2021 as one of the most important features of that year. Still, we had to wait until macOS 12.3 for the feature to actually become available, initially only as a beta feature. At the time, Apple couldn't promise it was working properly. We are now a few months further and the most important bugs have been removed. Apple indicates that Universal Control is no longer in beta as of macOS 12.4 and iPadOS 15.5.
There have been few complaints about performance or functionality lately. iCulture editor Daniel:
I've used Universal Control several times and I'm really happy with how it works. I have also been able to do something useful with it several times.
With Universal Control you can control multiple Macs and iPads with the same mouse/trackpad and the same keyboard. This way you can easily switch between devices. In the tenth beta of macOS Monterey, Apple was already preparing for Universal Control, as shown below:
It was then still uncertain whether it would be in the final release of Monterey, which appeared in the fall of 2021. This appeared to not be the case. Apple did the same with iCloud Private Relay, which was already usable, but also had a beta label. Another feature we were really looking forward to at the time was SharePlay, which became available a little earlier.
You could force-enable Universal Control at the time by going to System Preferences > screens to go. You then saw an option to let others control your keyboard and mouse remotely. You couldn't use it yet, but the fact that it was an option in System Preferences gave the impression that Apple was busy working it into the release. If you had two Macs running on Monterey, you could enable Universal Control by modifying internal system files, but you still had to be aware of bugs. Thankfully that's all over with the beta exit.