✅ Fixed: the moved quoted button was the problem for me. I saw it now by accident.
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Does anyone else have issues doing quote posts with @apps ?
It always worked, but it's not working anymore.
I already deleted and reinstalled Fedilab.
I tried the official Mastodon app, and there it worked, so it's not a problem with my account.
Asking first here before filling out the bug report tomorrow.