Hi, I had an issue with my computer and had to completely renew the software. I have got my Byteball wallet seed but no backup file.
Do I understand it right, that my blackbytes are gone?
Correct. If you didn't make a full backup and didn't save the data directory, your blackbytes are gone.
or where are/were they saved?
From
https://byteroll.com/backups :
macOS:
~/Library/Application Support/byteball
Linux:
~/.config/byteball
Windows:
%LOCALAPPDATA%\byteball
When I try to backup my GBYTE using the seed it say I need to use full wallet. Can I just download full wallet (currently using light, old one was light as well).
Download the normal wallet (which you have already), and set it to "full wallet" when you create a wallet.
It will take a while (up to days) to Sync.