I was under the impression that Go also uses Elo, then I did a bit of cursory research and discovers that it varies.

Two major federations are American Go Association (AGA) and European Go Federation (EGF). EGF uses an Elo-inspired update rule since 2021. AGA uses a quite-different Bayesian system without pairwise update; they provide a paper and a C++ reference impl.

Asian countries don't bother with such numeric ratings. Instead, rankings are titles which are won through tournament promotion structures (sounds similar to Sumo to me).

Interesting, because I always thought that it was more "apples to apples", and that the higher upper limits of Go rankings was somehow indicative of the higher "dynamic range" of the game compared to chess. For example, if Elo were applied to basketball, what would the Elo of Lebron James be compared to a playground hooper (leaving aside that 1-on-1 isn't the best part of Lebron's game)... would it be higher or lower than Magnus Carlsen in chess? I don't have an intuition.