I have had the same experience...
My feeling is that the problem you have, trying to open one of the effect rooms, might have to do with what looks like an inventory system, that should make opening and switching between rooms faster. It does that in my system. CL apparently introduced this inventory approach over the last few months and 365 versions. But this inventory needs to be build from a stable position. So, I would guess that this does not always goes will.
When I recently moved to another laptop, I had to rebuild windows (11) and installed the CL software, while I was doing that. PD did not work properly, whatever I tried. I think this was (also) because I tried to remove OneDrive, which during the PD installation was used as the default documents folder to store some PD files. So both running PD and removing OneDrive did not work for me. It was very clear that working with the various effect rooms, was not possible.
So, I uninstalled all CL software, made sure that none of the custom settings were kept (it is an option during the uninstall) and also made sure that I had a copy put aside for all the custom titles and other stuff I have made in all previous versions. After checking windows installation (updates etc.), drivers and so on, all the things you have already done. I first moved all the custom files (titles etc.) to the proper places in c:\users\%username%\documents\cyberlink\powerdirector\nn.n (that is the version number). If you have items from previous versions put them in place before the installation, but make sure that there are no PD 21 folders.
After that I installed PD with the Application Manager and tried to open rooms. It worked better. The first time a bit slower, because apparently PD was building an inventory (I am still guessing that is what they use).
So, PD 365 works for me now. But I also still get the accessional crash (which are sent to CL, so they should be in the know). They should still have some home work to do….