He is a free agent after the 2021 season and was drafted in the 3rd round so no 5th year rookie option. Therefore, not only would Dallas have to offer a haul in terms of a trade they would also have to pay Brown a hefty contract (for point of reference Baltimore paid LT Ronnie Stanley a 5-year $98.75M contract with $64.166M guaranteed with an average annual salary of $19.75M.
So, unless Dallas is going to offer something like LT Tyron Smith, WR Amari Cooper, and a draft pick (which I doubt Baltimore would consider seeing as how Smith is showing injury signs and will be 31 years old) I think this is all a pipe dream.
Besides, Dallas likes to hold on to their relics and overpaid players.