- for 6 and 9 handed, yes they can solve any 2 player scenario you give it. you solve to some expected loss (like 1%), so it's not a perfect solve. you can solve lower, but it takes longer. in theory there are multiway hands that are unsolvable.

- human players adapt to GTO by leaving the game. you are not beating a solver. solvers by their very design are unexploitable.

- sites can catch players that use solvers if they care to. in my experience there are sites that care and others that dont, depends on the market. regs know who is cheating.