I downloaded unity from flatpak before and it didnt work, after i installed it from .deb and still does not work
I'm not familiar with Unity but that error message sounds more like a file association error.
How exactly did you install Unity? I would recommend following the instructions listed in their website, following the steps indicated for an Ubuntu installation. Note that they only support Ubuntu 24.04, which is at a higher version that what Zorin OS 17 uses (Ubuntu 22.04) as its base, so this may not work either.
But here's where I show my ignorance about Unity, since this is the "Unity Hub". Is this in any way related? I can get it to run fine but then I have to sign in to get any further, so I can't test any further.
Because it is a Flatpak, maybe it is neccessary to use Flatseal to give that Program more Permissions.