I don't know, an offer that is 1000% of Dortmunds investment can imo be considered a good offer. Which would be 80m. I don't think Dortmund would go bankrupt, hell they even would have plenty of cash to spare after acquiring a replacement. United could afford it even in Covid times, Sancho would get his move, everyone would be happy.
I don't see why it must be 120m, or why they hire an intermediary and try to make United pay him on top of that. That just doesn't seem like respecting the players wishes but really only Dortmunds own interest.
As I said, Dembele had to go on strike as clearly Dortmund were not holding up their end of the bargain, same as now.