Not many of the old Gimp themes work well with Gimp 2.10 Where did you get the four black themes ?
As you found PSP plugins will not work with Gimp. Not much PSP does work
There are some .tube brushes converted to Gimp image hose (.gih) Patterns can be converted (at least I have some somewhere)
I would start afresh. Delete the whole gimp user profile C:\Users\"yourname"\AppData\Roaming\GIMP Start Gimp and it makes a new default version user profile, empty of previous settings.
New themes ? Start here: http://gimpchat.com/viewtopic.php?f=12&t=18492 (edit: start of thread) and tack a query on the end asking for recomendations or start a new thread there.
As you found PSP plugins will not work with Gimp. Not much PSP does work
There are some .tube brushes converted to Gimp image hose (.gih) Patterns can be converted (at least I have some somewhere) I would start afresh. Delete the whole gimp user profile C:\Users\"yourname"\AppData\Roaming\GIMP Start Gimp and it makes a new default version user profile, empty of previous settings.
New themes ? Start here: http://gimpchat.com/viewtopic.php?f=12&t=18492 (edit: start of thread) and tack a query on the end asking for recomendations or start a new thread there.