[audiaudio]

Group the BV tracks, then pencil in volume automation on one of those tracks. All others in the group will follow.

To edit individual tracks, deactivate the group, then edit one track at a time.

You can make separate groups for 20 tracks and for 6 tracks, activating|deactivating each group as needed.

Another way: buss 20 tracks to a single aux. Put volume automation on the aux only. This works well if you are using plugs on 20 tracks. You can instead put plugs on only one aux track instead of 20, saving a lot of DSP.