[setsewerd]

Late response here that might not be useful to you, but I mostly use Google docs for lyrics (on both my phone and laptop) and tend to rely on bullets for alternative lines.

This is fine for 1-2 alternate versions of a given line, but would get clunky beyond that. I imagine if I wanted to fork a song further than just a few alternate lines, I could insert a 2-column table and continue the song in each column.

It's rudimentary, but if you're worried that making your own software for it is just a form of advanced procrastination, something like Docs might be more manageable than Keep.