Have you installed GHPythonRemote in Rhino 8? You need to give it an explicit path during the installation step, the latest version will only look for Rhino 7 installations and earlier:
python -m ghpythonremote._configure_ironpython_installation "%APPDATA%\McNeel\Rhinoceros\8.0\Plug-ins\IronPython (814d908a-e25c-493d-97e9-ee3861957f49)\settings\lib"
If there is any error at the end of this step, it is not fully installed and will likely not work.
In general, all of this should still work in Rhino 8 just like it worked in Rhino 7, but I only provide very limited support at this point. There are better ways of calling Rhino and Grasshopper functions from Python in version 8, including Rhino.Compute and Rhino.Inside CPython.