I am not sure about a lot of things .... but as far as I know any Shimano 11-speed anything fits with any 11-speed anything else ..... since you are using thumb shifters, why couldn't you use any Shimano road or gravel chain ring (46 teeth or more) and any Shimano cassette with whichever derailleurs and shifters (as far as I know, nowadays everything over 10-speed MTB is all compatible ... but i warn you my information id a decade out of date.)

You could use any road or gravel double and simply remove the inner ring, and run the derailleur as a chain-catcher---you can leave of the front shifter (and cable---weight savings ) and have a homegrown 1x with the gearing you prefer. Use the left-hand bar for your extra-long dropper seat post actuator.

I mean, the first 1x systems weren't bought from Shimano, they were made by guys who mixed and matched and wrenched to get what they wanted. it is loads easier nowadays ......

In all likelihood you could keep your existing 8-speed chain ring and run an 11-speed chain---it would be the first thing I'd try. Install and 11-speed rear end, drop the inner ring, uncable the derailleur, and see if the chain sticks too much. Since you won't be shifting up front, I'd bet it would run just fine. If so .... save bucks. If not .... oh, well, buy an 11-speed road chain set and strip the inner ring.