Can a 5G modem work on USB2.0?

We need to design a device based on Raspberry CM4 with a 5G modem (it must be a 5G modem) but unfortunately we do not have a USB 3.1 port because PCIe is used to support the SSD drive.

Will 5G modems work on USB 2.0? I don’t care about high transmission speeds.

Yes, why not? The host system has no knowledge about “G”.