Do you know any chess GMs or IMs with a tested official IQ score less than 100?

Easy: IBM Deep Blue

I was thinking the same @giords , and AlphaZero and Leela Chess 0, and Stockfish NNUE, but i guess they don't have grandmaster titles.

I'd say that it's a technicality :D
Stockfish currently achieves an ELO of 3544, I think it is reasonable to think it would be able to obtain a GM title, if given the chance :P

@giords This question was clearly about human players, because we don't have IQ tests for computers(yet). Your response itself was based on a technicality :D

On a more serious answer, I think some strong chess players could easily be not very smart.
Chess is a lot about pattern recognition and memory, if you have plenty of those you don't need brightness.
Which is exactly what a computer does, pretty much.