While I agree with others pointing out the oddity of a portable server in general: this sounds like a great use-case for a laptop.
Built-in battery, wifi you can broadcast out as a hotspot, and it even has a display/keyboard/mouse for troubleshooting!
An older laptop with the optical drive stripped out could have a 2.5” 5TB HDD in addition to the boot drive for some decent mobile storage.
The same apps I always used no longer work because of OS requirements. The “download older version” feature is extremely hit and miss (mostly miss).
The device works fine and is functionally useless because Apple said so. That’s not cool with me. Android might be just as bad, I don’t know — I’m sticking with FOSS mostly these days and just don’t have a working tablet anymore.