Good luck.
The lender doesn't want to do it for obvious reasons (why carry that paper at 3 when they don't have to. The seller is going to want you to make sure that you pay the mortgage so they are going to want it out of their name (and you are going to have to pay them the delta between what you are taking over v the sales price), and your term will be sort of jacked up.
Now- there are people who are not doing mortgages assumptions with the actual company that holds the mortgage, and just doing a wrap, but then you have to trust the seller to actually pay the mortgage or the home gets foreclosed upon, and you still have the issue of cash differential between sales price and mortgaged amount.
2024 saw 4.62M home sales. The FHA and the VA both had record years for assumptions at over 5,000! Many lenders (that will allow for them) take over 100 days to figure out how to get them done- 45 seems to be rocking and rolling. Maybe your seller wants the hassle that goes with that. Also- note only FHA, VA and USDA loans are set up to be assumable, typically conventional loans are not- but I have seen an odd one here or there advertised- that would be servicer dependent- but go back to the second sentence in my post with "lenders don't want to do it for obvious reasons".
Do you have to do a contingent offer? With a 2.85% mortgage in Dallas is that a house that will cash flow and makes sense to keep as a rental?