Discord is the only way to get updates, since Itch doesn't have a feature for saving or following jams, outside of joining the jam. Joining jams will give you an update when it starts by email if you have that enabled, though I don't think you get a notification on itch itself.
If you're interested in upcoming NSFW mini jams, the best I can suggest (that is not a Discord option) is that you save the URL and check back around the second Week every month. The URL generally stays the same so you can just add one to the number like 27 -> 28 and https://itch.io/jam/nsfw-minijam-28 will be available, likely in the second week of April.