BTRFS on Linux (including the SD card in my Steam Deck, dunno what the root storage on that uses). NTFS on Windows (BTRFS driver for Windows isn’t quite as stable as I’d like it to be). ZFS on a NAS because that’s how it came set up and so far the zRAID hasn’t failed me yet. FAT32 for UEFI boot partitions and recovery USB drives.
XFS at work because apparently ext4 isn’t “mature enough”. Not by choice.
No idea what Android uses, probably ext4 with some software on top?