This is a very good question, normally it would not have been a huge issue if they can convince the PoE officer they are here genuinely only to visit.
However with COVID, there are multiple hurdles - anyone already holding even a B1/B2 visitor visa & ESTA countries are currently not allowed entry into the US without a NIE (national interest exemption) which is granted by DoS i think
see here:
https://de.usembassy.gov/covid19-faqs-for-visas/
So I do not know / cant say but i am pretty certain they will NOT be allowed to enter.
I think only US citizens & Green Card holders are allowed back in the States. And those others who hold the NIE waiver and others like Airline Pilots , Cabin crews who are here mainly only for a day or two.
Expect a huuuuge backlog, My parents DQ is March 2020 and there is 0 update after their DQ last year....this is unfortunate...