First: there's a typo - it shouldn't be "Involved peoples" but "Involved people" in both tag editors.
Second: "Involved people" and "Musician credits" are grayed out for at least MP3 and Vorbis files.
I can edit both tags, but they're really hard to read.
The spreadsheet editor works well.
Fixed in: helium_12.0.14094.0.exe