What you've heard is correct. Pixel phones do not support HDMI or DisplayPort out of the USB Type-C port. What we're talking about is the DisplayLink Presenter app and DisplayLink compatible docks.
I'm simplifying things here, but the DisplayLink Presenter app basically scrapes your screen, compresses it into a USB data stream, that is then reconstructed by a DisplayLink dock or dongle, turned back into a video signal, and then displayed on the screen connected to said dock or dongle.
If your goal is to take things like Netflix, Hulu, Disney+, or any other streaming service that uses protected video and play them on a larger screen, it won't work. These apps view the DisplayLink Presenter app as a screen capturing app (because it is) and will only display a blank window on the other end. The only videos I've ever gotten to work are YouTube (through NewPipe) and videos I've ripped and saved to my phone and played through VLC.