The sidedness marker is only referring to physical side, not logical side. By marking extralib as a SERVER dependency, you are telling forge that it should only check if extralib is present when on the dedicated server. That means if you start up a modpack with extraquests on a client, it will not tell you that you are missing extralib when it should.

This should be marked as BOTH to fix this. I only looked at the 1.20 version, if that's how you've marked it on the others you'll need to change them as well.

Will be fixed in the next release.