So I finally got around to upgrading my NextCloudPi to version 20 with the hub and all. I really like it so far.
It also seems that I bumped into a know issue. All of a sudden I could not upload files over 8kB. It turns out that for some reasons the sys_temp_dir in /etc/php/7.3/php.ini had shifted from my USB media (a portable HDD) to the default location (/var/www/nextcloud/tmp) during the upgrade. After a quick move back to /media/USBDrive/data/tmp, everything is back to normal.
I found the solution over at the nextcloud forums.