While for the vast majority the deadlines may have passed, you can still apply to certain schools. Before wasting time and energy, communicate and ask if they are still “open” to considering your application.
Nothing is impossible. Now if you had your heart set on one school…that is a different issue.
My son is on a few WL (our error as being too narrow originally). He is now going one by one and to be honest, it is a much calmer and relaxed process. Admissions no longer have 1,000 names thrown at them.
Schools have no obligation to go to the WL. If they get a very good applicant in April and they have space, they will consider it.
Just make sure you do have a school set in the fall already!