How do you insulate a stud bay that's full of wires?

Don't skip the bay. The wires being surrounded by insulation is not a problem, that whole 'wires need open air' thing is a myth for this situation. NM cable is rated to run buried inside insulation, that's normal residential construction. What actually matters is that the cables are secured and supported so they're not just hanging loose in there, and that you're not covering anything that's supposed to stay accessible, like a junction box or a conduit body with removable cover. If that conduit has a fitting with screws on it, you need to be able to get to it later, so either leave a small cutout around it or plan on an access plate when you close the wall up. What I'd do is split the batt lengthwise so you've got two half-thickness pieces. Slide one behind the cable bundle against the sheathing, then lay the other half in front so the wires sit in the middle of the insulation instead of being squished under a full batt. The cables will naturally nest in the fluff that way. For the spot where the conduit runs along the stud, just rip the batt into narrower strips and tuck them around it. It doesn't need to be pretty, fiberglass is forgiving. Before you insulate though, take five minutes and staple that bundle up so it's not flopping around. You can get multi-cable staples that hold two or three NM cables at once, or those plastic clamps with the nails. A few staples along the drop and you're done. It also makes it way easier to see what you're doing when you're fitting insulation around everything.

Since it's a west wall in Texas getting baked all afternoon, that one bay matters more than you'd think. A cold stripe in an otherwise insulated wall is exactly where you'll get condensation and hot spots. Even a half-thickness batt back there is a big improvement over bare studs, and the wires will be happier sandwiched in fiberglass than they are in a hot garage wall with no insulation at all.

Agree with all that, and here's the one thing I checked on my own shop build before closing it up. Code lets a cable run thru thermal insulation without any ampacity correction as long as it's not buried more than 24 inches total. So don't stress the sandwich itself, just eyeball where that drop crosses the bay and keep the fully buried section under that length. Mine ended up being maybe a foot and a half of actual burial, no issue. If your bundle wanders all over the bay, that's the time to shorten the route rather than fatten the insulation around it.

I ran into nearly the same thing last fall on my shop wall, and what worked better than tucking batt strips around the conduit was cutting foam board strips and sliding them in behind it. A utility knife and a scrap of 1 inch rigid gives you a much tighter fit in a crowded bay than fiberglass ever will, since the batt tends to fold and gap right where the pipe passes through. Another thing I'd check first is wheather any of those cables are actually low voltage stuff like coax or ethernet mixed in with the romex, because those don't care about heat at all but they'll never stay put under a staple meant for heavier cable.