Unable to create subclass for legacy content

I have made many homebrew subclasses throughout my time on DND Beyond, which are all currently listed under the legacy content. After a couple-month stint of not making homebrew subclasses and the 2024 ruleset being implemented on DND Beyond, I created a subclass today that can only accessed on the new 2024 iterations of classes rather than the legacy versions of the subclasses I intended it for.

I am a little confused about how this works. There does not appear to be a toggle on the subclass page for which rules I would like to create for. Is there something am I missing? If not, is this a change that can be made?

To expand on wagnarokkr’s completely correct answer, please see the General Homebrew FAQ, question #5: (https://www.dndbeyond.com/forums/dungeons-dragons-discussion/homebrew-house-rules/131411-a-homebrewers-how-to-faq#GeneralHomebrewFAQ&BasicTroubleshooting).

Oh, okay! I don't mind copy and pasting it over. I'm glad that it can be done. Thanks for the response and the help.

I'll scour that forum if I have any other questions. Thanks!