I just checked, and the FWL13 Linux subforum wants 2 tags for me as well. On the latest Firefox available for my distro. Are you on Chrome?
And of course, you are unable to select 2 tags once you are in the Linux subforum.
Whereas the Framework Laptop 16 Linux forum only requires 1 tag
And the Framework Laptop 13 forum also only requires 1 tag
So perhaps a FWL13 Linux subforum bug that is not present on Chrome?