Hi Suep
Yes, you can use your support letters from 2 years ago. Just state that many of your appointments have been suspended because of COVID which is why there aren't any for the present time. Many people are in that position and it should be obvious, but it's always best with the DWP to state the obvious to them.
The length of your award has become very common and is happening to people regardless of whether their condition will improve or not.
BIS
Nothing on this board constitutes legal advice - always consult a professional about specific problems