you can pay a combined estimated tax payment.
should you file separately for 2021 here's what the IRS says about splitting joint estimate payments
ALLOCATION RULES
when a joint declaration of estimated tax is made, but a joint return is not filed for the same tax year, the payments may be treated as being made by either spouse, or may be divided between them in any manner agreeable to them. However, if the spouses do not agree to a division, the payments are to be allocated to each of them in the ratio of each spouse’s separate tax to the aggregate tax imposed.
