If you are significantly affected by any part of the current situation you can make a claim for mitigating circumstances. The University is not considering Covid-19 as a universal case for mitigation, but different people may be affected in different ways. You would need to explain the specific things affecting you.
Help and Support can offer advice and can review your claim for mitigating circumstances before you submit it.
If you have difficulty getting evidence due to restrictions on GP attendance and workload, contact your School in the first instance and clearly explain what you can get, anything you cannot get and the reasons why.