In the manual you say about shared groups:
“REAPER does not provide a similar feature and all clips are created as separate copies.”
This is not true. In Reaper this is called “Pooling” and there is a specific command to it:
Item: Remove active takes from ARA edit pool (unpool)
You can also press the little pool icon on the clip itself t remove from pool:
Unfortunately if you unpool an ARA item now in Reaper, the new item’s contents in Synthesizer V will be empty. Unpooling should work as detaching a group in SynthV, the previous contents should remain, so you can modify it without having to copy / paste back everything. The current method actually defeats the purpose of dissociating “shared copies”, since what It really does, is just create a new empty group. It does not “detach”, it deletes.
Also there is now currently no way in ARA mode, to copy / paste clips without pooling them.
And then if you unpool, your new clip will be empty.
Either there should be a way to copy paste without pooling, or unpooling should retain old content. This is a big workflow killer.