What is your question?

If it is whether the loss can be claimed on a 2020 return -- yes.

To claim a loss on the preceding year’s return, a taxpayer must make an election on the 2020 tax return by completing part I of Section D on the Form 4868. This election to treat the disaster loss as if it had happened in the preceding year must be made within six months of the original due date of the return, meaning any losses claimed on the 2020 tax return for a disaster that actually occurred in 2021 must be filed by October 15, 2021.

Or is it whether that 10% floor on Form 4684 applies?

As you found in Pub 547, "However, in order to qualify under this expansion, the major disaster must have an incident period beginning between December 28, 2019, and December 27, 2020 (inclusive). Further, the major disaster must have an incident period ending no later than January 26, 2021."

These dates have to be updated by legislation and apparently the Texas delegation has turned a blind eye to the need for negotiation on that update.