I escrow my mortgage payments on my new primary residence
To clarify, mortgage payments are not escrowed. Things like property taxes and insurance are escrowed, and what gets deposited to that escrow account is included in your mortgage payment each month.
I reimbursed at closing the seller for real estate taxes they previously paid
What you reimbursed the seller, was for the property taxes they previously paid, that cover the period of time starting from the date you purchased and closed on the sale.
These prorates taxes were NOT paid from my escrow account,
They never are paid from escrow at the closing. At least, its not shown that way on the paperwork.
do I COMBINE those pro-rated tax amounts paid at closing on my new primary residence with the real estate taxes I also paid on my prior primary residence (that I also sold in 2020)?
Yes, you can do it that way. You "should" receive a 1098 on the home you sold that will show the property taxes paid by you. Subtract from that amount, the amount you were reimbursed by the buyer of your old home.
On the home you purchased, the closing documents will show somewhere the property taxes you reimbursed to the seller. Those can be included in the total property taxes as figured in the previous paragraph.
If you didn't make an actual mortgage payment in 2020, then you probably won't receive a 1098 on the new home. Therefore, all your property taxes and mortgage interest you can claim are on the closing statements. If par chance you "do" receive a 1098 on the new home, then more than likely it's duplicating or including what's already reported on the closing statements. So be careful that you don't unwittingly "double-dip" on your deductible mortgage interest and property taxes.
