disabling transparency effects in guest helped with fixing the glitches but performance stays at the unusably low level
Guest: Fresh install of Windows 10 Pro 64-bit Version 2004 (OS Build 19041.264) + Virtualbox Guest Additions (installed not in Safe Mode) + VBoxSVGA + 3D acceleration + 256 MB Video Memory + 4096 MB RAM + 2 CPUs + WDDM 1.0 + DirectX 12
Still struggling with extremely low video performance and glitches after trying almost everything covered by related threads on this forum using: