I believe it requires sidecar lyric files, although I'm not sure which formats it all supports.

You might try something like this to collect them: https://github.com/f1nniboy/lrcmux

Would you mind sharing more about your experience with Simplefin? I've been looking to make the jump, but I've read a fair amount of feedback that seems to indicate it might not be worth it given issues with instability, inconsistency syncing, etc.