New signs can’t hang on barriers

Cannot reproduce, I was able to place hanging signs on the side and bottom of barriers. Unless you mean the fence block?

like that, I would like to do like the log behind

From the 22w42a changelog "Attached to the solid side of a block" Your issue here is that you are trying to attach the hanging sign to a non solid side the fence post.

Fences have no solid side faces, that's why you can't place them there. A solid side face is required to place them, that's not a bug.