Quick reply while I'm grabbin coffee. Honestly, I had some issues with that 35mm when I tried it last year. Unfortunately, the autofocus felt a bit clunky and it just wasnt as good as expected for fast-paced street scenes, especially coming from L glass. If you want to stay under that 700 dollar limit and be truly invisible, you really gotta look at the Canon RF 28mm f/2.8 STM. Its a pancake lens and basically disappears on the R6 body. Just gotta ask tho, do you find yourself shooting mostly at night or during the day? Because the 28mm is tiny but that f/2.8 might be a struggle if Chicago is gloomy. You could even pair it with a Canon RF 50mm f/1.8 STM and still have plenty of cash left over for your trip.

Late to the party here... been shooting street for years and I am super satisfied with my R6 setup. Before you drop the cash tho, quick question: what focal length do you usually favor on your zoom? Do you prefer having more of the scene or isolating subjects? Honestly, grab the 50mm 1.8. It is tiny, costs next to nothing, and works well for getting those candid shots without being noticed. Quick tip: use the savings on a low-profile wrist strap. It makes you look way less like a pro photographer and more like a casual tourist, which is exactly what you want in Chicago. No complaints with that combo on my end.

Honestly, I went through the same thing when I first got my R6. The 24-105 is a beast for portraits but it is basically a neon sign saying I am taking your photo, which kills the candid vibe. I picked up the Canon RF 35mm f/1.8 Macro IS STM hoping it would be my savior, but unfortunately, it was a bit of a letdown in terms of build quality. Compared to your L glass, the plastic feel is definitely noticeable. It feels cheap. Plus, that extending front element is kinda annoying for street work. It is not as weather-sealed as Id like, which is a bummer if you get caught in some Chicago drizzle. Focus is loud. I was pretty disappointed with that. If you can get past the plastic feel though, it is probably the most practical choice. 35mm is the classic street focal length for a reason. I tried the Canon RF 50mm f/1.8 STM but it felt way too tight for busy downtown areas. I found myself constantly backing into traffic just to frame a shot. Not fun. If you really want to be invisible, look at the Canon RF 28mm f/2.8 STM. It is a tiny pancake lens that makes the R6 look like a toy. It is not as fast as the 1.8, but it is so small people just assume you are a tourist instead of a pro. Just dont expect it to feel like your L series lenses... it is a major step down in terms of how it feels in the hand.