In my case it helped to set the scale factor to 100%. Thanks. I'm using three Samsung at 2560x1440. I posted this bug to the team and they are looking for a solution. Keep your fingers crossed.

Hi Mark, a workaround might be to set the screen scale factor to 100%. For me it did speed up the GDL Editor. Good luck. The same problem was posted in https://community.graphisoft.com/t5/GDL/GDL-editor-AC27-far-from-being-usable/td-p/581752 some tim...