Hi @Czaja,
Have you opened any Grasshopper documents in this Rhino session? Have you opened a VisualARQ document with Grasshopper styles?
There is a known bug in Grasshopper for Rhino 8: each time a Grasshopper document is opened (even if it’s in the background like in VisualARQ GH styles), a mesh provider is registered, which slows down Rhino viewports, especially the first draw. Closing the documents doesn’t help, as the mesh provider keeps registered. The more GH documents opened, the slower the Rhino display will be.
There are similar reports:
I’ve already reported this issue to McNeel and David is already looking into it:
https://mcneel.myjetbrains.com/youtrack/issue/RH-80348/Slow-selection-and-lags-when-rotating-view
Enric