Update: uninstalled Workstation 16 and installed backrevved version 15.1.1, and...  the VMnet0 auto-bridged adapter is back (attached), and so is the bridge protocol service. I was able to set auto-bridging to one adapter, then create VMnet2 and assign my dedicated second NIC, as normal.

Feeling like a bug with WS16. Keeping the rev at 15.5.1 for now to fire up my VM's and get some stuff done, but will try to see what happens when upgrading to 16 soon.