Indeed, GB will definitely win more than 20 gold medals.
In swimming events they have realistic gold chances with Duncan Scott in several events, Adam Peaty in the 100 breast and the 4x100 medley men and mixed.
In track cycling they will probably win all the events, but normally for sure women's omnium, madison, men's sprinting and pursuit.
In rowing they have 6 very strong teams in the men's four, eight and double sculls, and women's light double sculls, quadruple sculls and pair.
Only in these 3 sports I already count 14 gold medals. And don't forget GB has a very strong women's football team, I think GB is a team that can surprise the US.