[moenk]

That's because your PDVD filetypes are not exclusive.  They share common filetypes with the 4K iso's you want FAB to open exclusively.  Just because you're using a filename for FAB, doesn't mean PDVD filetypes are going to be ignored.  Every PDVD rule you have is the same for a 4k iso so all of them are common.  Fwiw, FAB doesn't match refresh rates unless you manually change in GPU settings before playback and you'll need to put it back after - not ideal imo.  Also, the Kodi internal VideoPlayer handles 4k iso's with menus but read my post above yours.  So do other external players but without menus.  If you insist on using those two players, perhaps use a unique filename for "HDR" assigned to FAB and another for "SDR" assigned to PDVD but you'd have to rename all your iso's.  I'd test a few first to make sure the PCF.xml can handle two filename rules because it might not.  If it does, I'd flip the two rules one before the other and make sure that doesn't make a difference either.

Thank you brazen1 for all your suggestions. In fact thanks to your detailed tutorials I have learned how to use an external player embedded in kodi.  About playing uhd iso inside kodi itself, it will be an alternative but personally I prefer to do it with FAB because of the menus. From the tests I've been doing, PowerDVD doesn't play them due to its nonsense restrictions on the uhd specs with menu. For example my 11th generation processor is not supported according to the current specs they have because they only support playback and support this playback from 4th to 9th generation processors, or something like that. It is a significant example of the nonsense of these developers. About DVDFab not assigning the refresh rate automatically, doing a test with some uhd full, the truth is that the playback was quite smooth with few frame jumps and it was perfectly enjoyable. Well, now that you mention it, maybe PCF.xml doesn't quite support assigning dual media for external playback. I think it's very clear in the example above that only files with the name uhd are assigned to the FAB and all the others with whatever extension are played by PowerDVD. I've done several tests and I haven't had any success in any of them. If I don't find the solution, I'll leave it like this, because at least I can assign the playback via context menu. As you can see neither of them need any .bat to load the iso's as both players are self-contained to support .iso loading without any other third party software. 

Curiously, I changed the order of these two rules in the .xml and kodi didn't recognise either of them, so kodi played all formats. Very curious about the syntax rules of this file. Specifically the behaviour was due to the exchange of these two rules.

<rules action="prepend">
    <rule filename=".*uhd.*" player="DVDFab"/>
    <rule filetypes="iso|bdmv|mpls|m2ts" player="PowerDVD"/>
      </rule>
  </rules>
</playercorefactory>

If getting this combination to work involves me renaming the whole library, then I'd rather leave it like this. I also wouldn't know how to rename it properly to get the behaviour I want.