Plug-ins (binaries and Python) you have for 2.10 won't work in 3.0. They have to be rewritten/converted(*). And in the general case this also applies to any non-trivial script-fu script.
(*) For Python, because the GIMP API has changed, but also because we go from Python v2 to Python v3 and the language is a bit different (for the better, I'd say)
(*) For Python, because the GIMP API has changed, but also because we go from Python v2 to Python v3 and the language is a bit different (for the better, I'd say)