you did not clearly mentioned What are you looking for mate , What do you mean by Betting exchange using cryptocurrencies?
is this some sort of gambling sites that you can use as trading platform as well?
because you have just mentioned like Fiat betting.
OP already gave an example which is Betfair and afaik they're one of the biggest betting exchanges. The example alone is enough to give an idea of what he's looking for but I guess a lot of gamblers don't use betting exchanges. Also he mentioned "for fiat" because the site only accepts fiat deposits.
actually you can get some good crypto gambling betting exchanges by looking at some of the threads here and maybe you can also consider gambling sites that do hold bounties in the current forum, fortunejack, rollbit are gambling sites that are widely promoted by members here, but if you are If you want to try a different gambling site and offer a large selection of games, of course you can try to access
https://www.bk8crypto.com/ which is one of the biggest and most trusted gambling sites in Asia today, besides that BK8 is also a gambling site which already has an official license from PAGCOR (Philippine Amusement and Gaming Corporation) and is also licensed by the government of Curacao and Malta.
There's no need to suggest casinos and sportsbooks when OP already said he's going to use exbet.