The config file used to include the ability to adjust the spawn rate of structures (such as in 1.19.x). For 1.20.1, it's missing. Could it be re-added or is there another factor involved?

I also notice that it's a different file type (.json5, instead of .toml), and it isn't configurable through in-game (using the Catalogue and Configuration mods), but I believe it used to be.