“Some of them” may by chance end up not selected if you really put too many in, but generally yes; you just get noisier/smaller areas of each biome (*)
In the case of creative worlds, there is no weighting of the tiers so they will largely speaking be shoved in equally (some biomes internally specifying biases to their weight to make them a little larger/smaller which is respected by the generation system; but ignoring that).
in the case of sovereign worlds, where it asks you to say: “select at least 6 level 2, at least 4 level 3, at least 1 level 4” then it is expecting a ratio in the biome levels of 6:4:1. If you actually select biomes in a ratio of 6:4:20, then the level 4 biomes in this case would be weighted down by a factor of 1/20th so that if you summed up the land area of each biome level, you would get roughly 6:4:1, but each individual area-sum of the level 4 biomes will be 20x smaller than the level 2 and 3 biomes… this is effectively to prevent “gaming the system” by doing the opposite of the system wanting a 6:4:1, but you choose a ratio of biomes of 30:4:1 to try to make the world “easier” than its supposed to be.
(* in my case I did something like a sovereign wanting 6:4:1, but actually chose 6:4:40 and maybe 3 or 4 of the 40 biomes that were massively weighted down ended up not appearing at all, but the rest did)