What version of MuseScore is used to make the mscx files using the pdf import function?

I've used the pdf import function. My problem is that my go-to version of MuseScore is version 2, because it has a bunch of custom plug-ins I designed myself. When I try to import the mscx file into version 2, I get an error saying that the mscx cannot be read by the older version of MuseScore. I could of course use MuseScore 4 and export the results, however messed up, to mxl and import that into version 2, but my question is, Are the mscx files readable by version 3 (which has more plugins that I can model my custom plugins after).