I tried to follow previous guides about homebrew subclass building and options and whatnot, but now the entire feature doesn't show up in the character builder, and yes, the hide in builder setting is off.

Did you create it as a “granted” feature, or as a “additional” or “replacement” feature? It should be granted.

granted feature, and I've experimented with clicking the granted option on the optional features (which I know wasn't correct, was just trying to mess around with it to see if it'd work)

After you added it, did you remember to re-save the entire subclass using the main [SAVE CHANGES] button under Basic Information? If you don’t the system won’t pick up your changes. After that it can take up to 20 minutes for things to update.