In BIAB, you can only edit one track at a time; and as you have discovered, you can display multiple tracks.

While it's possible multi-track editing could see its way into the program, I doubt it will happen any time soon, so I recommend using a dedicated notation application for your score.

There are many available at various price points:

MuseScore (free)
Noteworthy Composer
Presonus Notion
MakeMusic Finale (and the less expensive PrintMusic)
Avid Sibelius (and the less expensive Sibelius First)

and others.

All of the above support MIDI export, so you can export from the notation program and bring the MIDI into BIAB. Likewise, they support MIDI export, so you can also do the reverse - export from BIAB to MIDI and then import into your notation program.

Bringing multi-track MIDI into BIAB and separating out the parts is tricky, because other than the melody or soloist track, the other tracks are generally regenerated based on the style, not a static MIDI import. But doable, and was discussed in a recent thread.

I have all of the above (well, I don't have Sibelius First, but I do have Sibelius) and generally I use either Noteworthy Composer of Presonus Notion for my scores.

John

Laptop-HP Omen I7 Win11Pro 32GB 2x2TB, 1x4TB SSD
Desktop-ASUS-I7 Win10Pro 32GB 2x1.5TB, 2x2TB, 1x4TB SATA

BB2025/UMC404HD/Casios/Cakewalk/Reaper/Studio One/MixBus/Notion/Finale/Dorico/Noteworthy/NI/Halion/IK

http://www.sus4chord.com