Pretty much as the title. I have some old assets that come with specular/glossiness maps. Do I need to convert them to metallic/roughness first to be used in Principled Shader VOP? Or is there a PBR shader supporting specular/glossiness workflow?

Roughness is just the inverse of glossiness, so you can invert your gloss map and plug it into roughness.
I wouldn't even bother with the specular map and just set the IOR appropriately.
Unless your spec map is defining areas of metal vs non-metal then just plug it into metallic.

Don't get hung up on the specific map names and just try to understand what they are doing and you can make it work.