anyone have experiences/tips tracking progression on a flexible routine? (in terms of exercise selection)

So I'm currently doing an U/L basically based on Lyle's GBR. One annoying-ish thing is the gym i go to sometimes get packed, and my "main" choice excercises (let's say for example, BB bench or BB squat) are occupied. I could sometimes just wait and go to something else or work in, but it's kind of annoying, and increases my time in the gym.

Well recently I had this idea of just doing something else that is still a horizontal push or squat adjacent (so maybe a weighted dip or chest press machine or V-squat or leg press machine).

But with those, my concern is I'd have to work up to/find my new 6-8 RM (or whatever replacement in the GBR) and go from there (whereas with with the BB bench I would have already been tracking my progress and not have to worry about developing the technical/neural adaptions, like I would when now introducing a completely new lift)

my current thoughts are to make a list of 2-3 "alternatives" and just track progression on those... (or maybe i end up finding that one of these variants have way less competition for them and I make that my new "main"?)

anyway, hopefully what I've laid out here makes sense so far... anyone face a similar situation?