Once Rhino 8 SR 7 is out we will likely be able to ship our plug-in such that it supports both frameworks.
Related issue in Rhino 8: https://mcneel.myjetbrains.com/youtrack/issue/RH-80648/Yak.exe-fails-with-multi-targeted-plugin
Related forum thread: .NET multi targeting for yak packages - #12 by snabela