Have you assigned that category to any transactions? If yes, then moving any money out of it and hiding it is the much cleaner solution. If you haven't used it for any transactions, you can go ahead and delete it.

If there’s anything in the Available balance then move it to another category (since you will no longer need money for this subscription) then hide the subscription category.

This way your budget is tidier (fewer categories) but you don’t lose the underlying info e.g. in your Reports you will still be able to see that you spent X amount on this subscription category in the past which is useful info to have when, for example, reviewing how your year of spending looked.