For that portable monitor, you should just need a cable with USB-C plugs on both ends which supports USB 3.0+ (could be branded as SuperSpeed, 5Gbps, etc). Nothing more complicated than that.
The baseline for a cable with USB-C on both ends should be PD up to 60W (3A) and data transfers at USB 2.0 (480Mbps) speeds.
Most cables stick with that baseline because it’s enough to charge phones and most people won’t use USB-C cables for anything else. Omitting the extra capabilities lets cables be not only cheaper but also longer and thinner.
DisplayPort support uses the same extra data pins that are needed for USB 3.0 data transfers, so in terms of cable support they should be equivalent. There also exist higher-power cables rated for 100W or 240W but there’s no way a portable monitor would need that.
This argument is even more ridiculous than it seems. During the copyright office hearing for this exemption request (back in April), the people arguing in favor of libraries talked about the measures they have in place. They don’t just let people download a ROM to use in any emulator they please. It’s not even one of those browser-based emulators where you can pull the ROM data out of your browser cache if you know how. It’s a video stream of an emulator running on a server managed by the library, with plenty enough latency to make it very clearly a worse gaming experience.
It’s far easier to find ROMs of these games elsewhere than it is to contact a librarian and ask for access to a protected collection, so there’d be no reason to redistribute the files even if they were offered, which they aren’t.
On top of that, this exemption request was explicitly limited to old games that have been long unavailable on the market in any form, which seems like an insane limitation to put on libraries, places that have always held collections of books both new and old.
All of that is still not enough to sate the US Copyright Office, the ESA, AACS, or DVD CSS. Those three were the organizations that fought against this.