If I had lots of medical expenses in 2021. but they are a debt. I haven't paid them yet. Do I still claim them as medical expenses or not?

You cannot claim as a deduction on a tax return a medical expense which you have not yet paid.

You deduct medical expenses in the year that you pay the provider, not the year that you incurred the expense or the year that you received the bill.

If you take out a loan to pay the medical expenses, you deduct the expenses in the year that you use the money from the loan to pay the provider. But if your debt is to the provider of the medical services, not to a bank or other lender, then you have not yet paid the expense and you cannot deduct it.