Oops, no, it dropped from 500 BM to 1.2 GB left available. Still something there…
root@pi-usenet:/# lsblk -o name,fstype,label,size,ro,type,mountpoint,partuuid,uuid
NAME FSTYPE LABEL SIZE RO TYPE MOUNTPOINT PARTUUID UUID
sda 4.5T 0 disk
├─sda1 vfat EFI 200M 0 part 81af391e-21b4-4209-b08f-50596cb73d75 67E3-17ED
└─sda2 ext4 4.5T 0 part /mnt/seagate fe20d7b3-df21-4b8c-8146-725513ad6fa8 fd516b8e-fab1-4569-9f35-2073f69a1cc4
mmcblk0 29.7G 0 disk
├─mmcblk0p1 vfat boot 256M 0 part /boot 8f4dbd00-01 4ADC-240F
└─mmcblk0p2 ext4 rootfs 29.5G 0 part / 8f4dbd00-02 89cef7ba-d45a-47e7-8d42-aff18afcec80