Proof of Funds are more common for investment properties or with investor groups. Pre-Approval or Pre-Qualification letters are generally used for residential homes to be occupied by owners.
I have professional and personal relationships with multiple types of lenders. When you tour homes with me or connect with me at an Open House, I am more than willing to introduce you to lender who may be helpful to you. I have loan officers for fix and flip, DSCR purchase or refinance, new construction, land only, or primary home/owner occupied, or doctor loans at the ready if you want guidance. Of course, you can always choose your own!