I can see where the confusion comes from. I would normally expect a release candidate to be fully functional, not missing several important functions (hot desking is the one that made me raise my eyebrows the most). To compound that, the update page also makes it look like you're going to V20 (no mention of release candidate on there, it simply says "Version 20 is now available. Before upgrading, take a full backup of 3CX and save it outside of the instance. This upgrade will also upgrade Debian from 10 to 12."). There is also no link to the corresponding blog post (as you usualy see for an update).
It would be very easy for someone to read that and update without realising there are potentially some very bad outcomes for their install.
In fact, the only reason I didn't upgrade is that I've been burnt by this sort of thing before (an upgrade took out pretty much our entire install because our phones were made end of life which you wouldn't know unless you read the blog posts).