Downgrade of linux-firmware seems to have solved the GPU freezes for me. The computer runs for at least almost two days without any problems.
CPU: Quad Core AMD Ryzen 5 PRO 3400G with Radeon Vega Graphics (-MT MCP-) speed/min/max: 1399/1400/3700 MHz
Kernel: 5.10.34-1-MANJARO x86_64 Up: 1d 18h 09m Mem: 5348.1/30077.2 MiB (17.8%) Storage: 1.59 TiB (38.2% used) Procs: 380
Shell: fish inxi: 3.3.04
gnome-shell 1:3.38.4+13+gcf9d73ed5-1
lib32-mesa 21.0.3-3
lib32-mesa-vdpau 21.0.3-3
libva-mesa-driver 21.0.3-3
linux-firmware 20201124.r1786.b362fd4-1
mesa 21.0.3-3
mesa-demos 8.4.0-4
mesa-vdpau 21.0.3-3