Do we still need to terminate the display port with Catalina?
You should not need to terminate the video port of your Mac mini as support for a headless machine is natively supported by macOS - Remote into Mac Mini after a reboot.  I say “should” because while it is supposed to be supported, I’ve run into instances where it would simply fail without it - notably VNC.
Bottom line is that you shouldn’t need it.  But, does it hurt to have it?  No.  It’s also sufficiently inexpensive that getting one so you don’t have to worry about any issues makes it quite feasible.