Follow this guide, partition your disk a install Pop OS 20.04 from live USB :
- Boot from live USB
- Partition your hard disk: EFI Boot, BTRFS root, EXT4 home, SWAP
- Install Pop OS and DO NOT REBOOT
mount -o subvolid=5,ssd,noatime,space_cache,commit=120,compress=zstd /dev/sdb5 /mnt