I ran adb shell and didn’t find blkid, lsblk, or anything that would help me determine the filesystem of the internal disk. mount and /proc/mounts report tons of stuff, but hard to decipher.
When I turned on config logging it reported fuseblk for both the internal disk, and the external SD card, which is exFAT formatted. I tried adding an ext4 formatted card, but it wasn’t recognized.