Hi Gabriell @Zeon ,
You actually have so-called ‘double Vertices’; you can see that the Bevel only goes along one Face.
The Edge that you are trying to Bevel, are really 2 Edges ‘on top of each other’. You have only one of them Selected and that’s the one that gets Beveled. It can onmly go into one direction, because on the other side it is blocked by the second Edge.
So, Select everything (with A) and then, M > Merge > By Distance.
