Looking for pouch with no other straps

Try amazon or wish for things like https://www.amazon.com/TiaoBug-Lingerie-Backless-Underwear-Underpants/dp/B0728J5N6G

I think Cocksox makes a posing strap too

Sometimes strapless thongs are called C-strings. Is this what you had in mind? Link below has some options https://bodywearformen.com/product-category/bodywear-for-men/underwear-bodywear-for-men/c-string-underwear-bodywear-for-men/