There aren’t many 5G mPCIe cards available on the market - until that happens, it’s quite unlikely that there will be a 5G Mudi.
The telephony part of the device is a swappable (not by the user, sadly, at least not easily) mPCIe card, which is why it’s so simple to support multiple markets.
Carrier support is based on the frequency bands used. In the US if I’m not mistaken, there are 4 carriers (well, now only three with the Tmo-Sprint merger) that have actual physical networks, the others are just piggybacking on these (the so called MVNOs or virtual mobile operators). You need to check the area you’re in for carriers and their specific bands, and then decide on the Mudi you need. The available cards are these for Cat6 which is faster, but more expensive, and these are for Cat4.
Given how the Cat4 modules are broken down into smaller regions, I’d recommend you go for the Cat6 North America one, however make sure that the carriers in your area support the bands listed!
Other than that, all you need is a nanoSIM card from the carrier, and you have internet.