Ah I see, I had fotgotten that your package introduces dark mode to the IDE. In this case, Laz3.0 will not resolve this issue, I compiled metadarkstyle and metadarkstyledsgn with 3.0RC2 - it works, but compilation of metadarkstyle226 with 3.0RC2 fails due to the IDEConfig package which is new in v3+.
Therefore, I think there is no other way than to distribute two version-dependent packages. Please ask GetMem if there is a possibility that OPM installs only the one for the current version and ignores the other one.