Comment 18 for bug 480159

Also noted here.
Lower resolutions make grub usable, but still slower than expected.

Ubuntu 20.04 LTS + grub 2.04-1ubuntu26
Lenovo Flex 14 AMD / CPU Ryzen 5 3500U / Integrated Radeon Graphics / FHD display

grub>videoinfo
 Adapter Bochs PCI Video Driver: No info available
 Adapter Cirrus CLGD 5446 PCI Video Driver: No info available
 Adapter EFI GOP driver:
 *Ox000 1920 x 1080 x 32 (7680) Direct color, mask: 8/8/8/8 pos: 16/8/0/24
  Ox001 640 x 480 x 32 (2560) Direct color, mask: 8/8/8/8 pos: 16/8/0/24
  Ox002 800 x 600 x 32 (3200) Direct color, mask: 8/8/8/8 pos: 16/8/0/24
  Ox003 1024 x 768 x 32 (4096) Direct color, mask: 8/8/8/8 pos: 16/8/0/24
  Ox004 1280 x 1024 x 32 (5120) Direct color, mask: 8/8/8/8 pos: 16/8/0/24
  Ox005 1400 x 1050 x 32 (5600) Direct color, mask: 8/8/8/8 pos: 16/8/0/24
  Ox006 1280 x 960 x 32 (5120) Direct color, mask: 8/8/8/8 pos: 16/8/0/24
 Adapter EFI UGA driver: No info available