A clearnet domain with only 4 letters is quite expensive. On Namecheap, mixy.net is available for $10k and mixy.io is $6k. There are cheaper options but I doubt anybody would fall for a fake mixer with a .beauty or .monster domain name.
You are right about domains like ".beauty" but also don't forget that scammers also like to use character substitution and similarity in the pronunciation of the keyword. Usually, when a new player appears in a niche, scammers quickly react and purchase similar domains, so in this case one of the effective methods is preventive action (that is, the mixer owners should be the first to buy as many similar domain names).