Nighthawk® AX4 4G LTE Modem + WiFi 6 Router SIM Compatibility

Hello! I have a question related to the Nighthawk AX4 4G LTE Modem WiFi 6 Router: https://www.netgear.com/home/mobile-wifi/routers/lax20/

It says in the SIM compatibility thing that has some certified mobile broadbands, as it comes: "Access 4G LTE on the cellular network as an alternative to wired internet. Now certified with AT&T, T-Mobile and Verizon. Select a data plan and activate a SIM card from your preferred provider1, or use the SIM card option included in box2. Not compatible with Sprint".

I haven't heard of those providers. My question is: will other mobile providers (like Vodafone, Orange, Digi or whatever that exist in Romania, the country where i live) be compatible with this router? From what have been written between the quotes, i understood that it is locked only in those providers and none others...

U can ask if u wanna understand more detailed. Please help.