I am not an RB user, but I do have a large collection of songs written with BIAB that include lyrics, both note based and a few old ones that are bar based.

I found it hard to believe that RB wouldn't be able to accept songs with lyrics or part markers so I followed John's advice and opened one of my existing note based songs in RB. It's is a "modern" pop/rock song, not a jazz classic. It has both Ral tracks, a real drum and a midi track. I didn't convert it to MIDI, WAVE, MP3 or anything else. I just opened the MGU file in RB.

It worked perfectly!! I have all the notes, it generated all of the accompaniment, the lyrics are all there, and so are the part markers. It took a while, much longer than BIAB to generate all the real tracks, but it completed successfully.

I do not understand how you can say it doesn't work.

BIAB for Windows Version 2019 (643)
Windows 10 (1909)