100% it's bud rot, I'm so sorry. I had the same thing on one of mine.
Be very careful when removing affected buds so you don't spread the spores to healthy plants, and cut more than you think you should because that shit lives inside the stems just waiting for the right conditions. Looks like it is many of your buds though so you may have to discard this baby altogether :( it's so heartbreaking I really feel for you 💔