Not sure if it has to do with connecting to external monitors, but I noticed my 2019 16” MBP click and right click stopped working shortly after hooking it up to two external monitors.
SOLUTION: what worked for me was oddly enough to just turn on a 2.4GHz mouse I had connected to it and then click worked on both my mouse and my trackpad.
When I turned it off again, my trackpad also stopped working. Then I restarted my computer and turned off the external mouse and the trackpad worked normally again for now.