A return of your contributions is not tax deductible because you won't be paying tax on the money you withdraw. You take the money out temporarily and don't pay tax, so the return is not deductible. In fact, the return is not a "contribution" at all, it is a return of a prior distribution.
Normally, if you want to return a distribution, you must do it within 60 days, so the issue of tax doesn't come up. With a COVID withdrawal, you can spread the tax out over 3 years (if you choose) and you can make the return for up to 3 years. That might mean you pay tax on part or all of the distribution in year 1, but when you return it in year 2 or 3, the tax you paid in year 1 will be reversed. But it will all work out in the end. Any part of the distribution that you end up returning will not be taxed once everything is settled.
