To work around macOS' awful monitor restrictions (i.e. lack of general MST support), we bit the bullet and got a Dell WB19TB [1] (Thunderbolt dock). It sucks from a wiring perspective but it works.

[1] https://www.dell.com/en-us/work/shop/dell-thunderbolt-dock-w...

(To those that go down this route, be aware: you cannot use both DP ports on this dock as-is -- again, macOS lacks MST support. One monitor must be connected to the Thunderbolt add-on module.)