There is a lot of new stuff in this release. The only OpenFX and VST2 plugins that will appear automatically for now are the ones listed. You need to install them yourself.
The UI generator for hidden engine effects and external plugins is not much supported either, hence the --experimental. When that is used the filter menu has an additional 
button that lets you pick something to try out. Choosing things in here does not add them yet as a filter. This is a configuration dialog for what to make available. You then need to locate what you chose (search) and add it. Be prepared to enter the twilight zone! You can expect a lot confusion like: what does this even do? Is the effect itself broken, or is the generated UI causing this–whether that is no apparent effect or obviously broken?
The main areas of concern for testing are around:
- do any external plugins cause a crash on startup
- the compatibility of the new completely video output (display) code that facilitates the features of external monitoring whether as an entire system display or the new Preview Window (HDR).
- compatibility of the HDR mode of the new Preview Window on a HDR monitor using HLG or PQ HDR videos (but not combining them)