Hi!

I converted a tube without caps into colums. Now every column is the same polygon. Is there a way to make every column a different polygon? I already tried Convert Line, but this creates connections on the top and bottom which I don't want. Thanks in advance!

you most likely set Primitive Type to Mesh, not Polygon (since it's impossible for disconnected poly lines to be part of the same prim as in your screenshot)
so make sure its set to Polygon