What matters to Linux operating systems (to their kernel thru system calls done by every programs) is not user names but user ids or uid-s. It is a small positive number (not a name), like 1234. Read credentials(7).
You need to ensure that on both your Debian and your Ubuntu the daniel user has the same uid. The daniel name is not very important (and you might, but need not, to use a different name). Probably Debian and Ubuntu are using different uid-s/gid-s for daniel. Read also id(1).
I assume you can get superuser power on both OSes, e.g. by running sudo.
The mapping between user names and their uid-s is often done in /etc/passwd, so read carefully passwd(5). BTW, that mapping could -with care- be done otherwise (but usually is not) and how it is done is configured in /etc/nsswitch.conf (which I assume you did not change, see nsswitch.conf(5) for more)
Likewise the mapping between group names and their gid-s is done in /etc/group, so read carefully group(5).
So, first run the commands (not GUI programs, in your case they are confusing you) to understand what uid/gid is used for daniel on both Debian and Ubuntu. You probably want to run the grep daniel /etc/passwd command (see grep(1)). Likewise, run the relevant command to find your gid (on both systems).
Then decide on a common uid and gid for both systems. It should be unused, and you need it to be the same on Debian and Ubuntu.