Hello!
(I bought a license today)
(MacOS Big Sur 11.3.1)
Everything worked at first. Then I needed to download some plugin, but python (runtime or smth) was not installed. I clicked to install it and restarted Glyphs, then it didn’t open and now the following message began to appear:
The Folder should be “Glyphs 3”. And are you sure you are in the right Library.
You can temporarily disable plugins by holding down Option +Shift when you start the app. That should give you a chance to remove the plugins from the plugin manager.
Oh, I really was in the wrong library. Now found the plugins folder and removed the Red Arrow, this one was there. But nothing has changed, the window still appears at startup.