Or USB drives period. My former employer didn't allow cell phones or really any device that could connect things from the outside. We had the Internet, but it all had to go through their own managed pipes.
Totally fine to bring in a monitor though. Not sure if that would still be true today, given the connectivity of things. I bet you could still bring in a monitor, but you'd risk needing to prove that there was no way it could do anything other than be a monitor.
I think there would be better luck with a dedicated monitor port (HDMI, DisplayPort, DVI, VGA), rather than a USB-C monitor, depending on how hard things are locked down.
Totally fine to bring in a monitor though. Not sure if that would still be true today, given the connectivity of things. I bet you could still bring in a monitor, but you'd risk needing to prove that there was no way it could do anything other than be a monitor.