5G USB Modem (maybe with external Antenna) for Slate AX GL-AXT1800?

I ordered a Slate AX GL-AXT1800, which I will primarily use for hotel traveling.
However, I would also like to use it on a remote property (in Germany) and need a 5G USB Modem with strong signal strength (preferably with an external antenna).
The paradox at this property is that the 5G signal is partly better than the 4G/LTE signal.
Are there 5G USB Modems that are compatible with the Slate AX GL-AXT1800?
The speed is not necessarily the most important thing there (although it would be nice if it brings a lot of speed), more important to me is a good connection.