Plasma 6 landed in opensuse. However, I recommend to do it in tty because if you do it in plasma the upgrade will be incomplete because the shell will crash in the middle of update without installing all. In case this happen to anyone, just reinstall plasma 6 pattern and it will go without problems
First logout of Plasma, then you can change to tty 4 (for example) with ctrl + alt + F4, then you can login there with your user and do the upgrade safely in that other tty (or another one if you want to haha, just not in the normal desktop).
I think the Plasma desktop is always in tty 3 (ctrl + alt + F3) and the Plasma login is in tty2, in case you want to go back.