Try plugging in the external monitors only on the left side of the Macbook.
tested with a $400 Targus thunderbolt Dock210 with two ancient Apple 30" Cinema displays in it;
tested with only 1 plugged into the dock, and the other plugged in separately
both scenarios work but ONLY when plugged into one of the Mac's LEFT ports.
I am using Intel Macbook pro 16" with Big Sur
Note that I did not need to install any drivers or software for the docking station.
chelms
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See my answer at https://developer.apple.com/forums/thread/666645?page=1#679566022 .
Basically, plug in both monitors (or dock with 2 monitors) only on the LEFT side of the laptop.
Agreed with @mjrnc, it seems plugging in displays only via the LEFT laptop ports gives the best results.
See my full answer regarding 2 external monitors with docking station at https://developer.apple.com/forums/thread/666645?page=1#679566022 .