Hi Albert,
I moved x42-plugins [1] to community quite recently.
After looking around I thought gmsynth was part of it, but apparently not (confused it with midigen [2])!
Still have to move quite a few packages out of testing, before I can tackle new ones, but I'll put it on the list!
Best,
David
[1] https://www.archlinux.org/packages/community/x86_64/x42- plugins/
[2] https://github.com/x42/midigen.lv2
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