Can anyone recommend with absolute certainty a bag that will host an 11.5” AR with a Law folder and a Surefire flash hider?

Preferably one that doesn’t scream “I’m tactical please target me first!”

Are you looking to keep the stock folded or not?

Tennis racket bag.

I got one of these and it fits my 11.5" AR easy. Not sure how much more the folding adapter and muzzle device add, but I've probably got an inch to spare in mine.

https://www.first-spear.com/noveske-discreet-backpack

I’d like to keep the stock folded

I've got 3 of these. A black 24" FDE 28" and just took delivery of an ODG 32"

Fantastic bags (for me anyway..) They might scream tactical more than you want though..

Savior Range Bags

Have you looked at the 5.11 Tactical AMP 72, it says the rear storage area is 24”H x 11”W x 2”D https://www.511tactical.com/amp72.html.  Also, here is a video and if you jump to 7:12 they guy brings out the bag and puts a DDMK18 with the Law Tactical adapter into it and it looks like it has about an inch or so at the top to spare https://www.youtube.com/watch?v=hNB77YpQe44 .  I just picked it up and like it a lot, I took the velcro molle off the front because to me it screamed "gun bag" and added one of their small organizer pouches on the front to cover up the velcro.  Pretty much looks like a regular backpack with plenty of room for just about everything.

I’m in the same boat and am considering the Vertx gamut 2.0 or Vertx gamut overland.
I think the Gamut 2.0 main compartment is 21” height and the overland is 26.5” height. Could always measure the AR when folder and look at dimensions of bags to see if it would fit

I've got a Vertx Contingency Duffel 45L that I use for a BCM 11.5 with a Law folder and a T-2.

Folded it fits into the side pocket with just a smidgen to spare or I can stow it in the top main section if I want to.

https://vertx.com/contingency-duffel-45l

Pretty handy bag with lots of spaces for storage and doesn't look like a "gun bag" to the average person.