I've always done upgrades and they usually worked, but updating across Android versions is quite painful. You need to be wary not to accidentally keep old versions of GApps and any other system modifications installed, and not all system services migrate that easily.
At some point, a transitionary .zip was published to help users upgrade between versions. However, I'm pretty sure their official policy is still that you should do a clean install.
I think upgrading between versions works (as long as you do it in order!) but your system will be a lot more stable if you do a clean install. The same can be said for any major OS upgrade, really, be it Windows 10 to 11 or Ubuntu 20.04 to 22.04.
Unless the major upgrade is Fedora, then it works great and is well supported to update in place for many years. The one major issue I had once was my fault because a force rebooted in the middle of the install. Still got it working though.
At some point, a transitionary .zip was published to help users upgrade between versions. However, I'm pretty sure their official policy is still that you should do a clean install.
I think upgrading between versions works (as long as you do it in order!) but your system will be a lot more stable if you do a clean install. The same can be said for any major OS upgrade, really, be it Windows 10 to 11 or Ubuntu 20.04 to 22.04.