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.