Pricipal home original loan back in 2013, remaining balance is about $800K in 2019.

Refinanced in 2019 to about $1M with cash out $200k to purchase rental property.

My understanding is that the loan dated from 2013, so $1M rule apples, interest from $800k can be deduct on Sch A.

Interest arrived from  $200k (excess of $800K) loan can be allocated to rental property?

According Pub 535: In general, you allocate interest on a loan the
same way you allocate the loan proceeds. You
allocate loan proceeds by tracing disbursements to specific uses