When I use the Selection Tool, the line only extends vertically on the track I am editing. Is it possible to extend the line across other tracks to help you line things up better? I don’t want to edit the other tracks with the Selection Tool, I just want the line to extend across them, so I can make more precise edits with things like a Rhythm Track.
No, but Audacity does have a “snapping” behaviour when you are lined up with audio clip boundaries or labels.
I made a plug-in for creating labels at “beats per minute”. The idea of this is that you can then quickly and easily create a label track that lines up exactly with a click track, and you can then line things up more easily with the click track. See this post: https://forum.audacityteam.org/t/beat-per-minute-labels/20785/1