Telia LT uses bands 28 (700MHz - low band) and 78 (3500MHz - mid-band). Both of these bands are supported by the TRB500 and were tested on the Telia LT network.
Please keep in mind, that since Telia LT uses a 5G NSA network, the service mode on the device must be set to either Auto or 4G + 5G, since setting the device to 5G-only will not work.
Another thing to keep in mind is that in order to achieve the best 5G speeds, band 78 should be used, as band 28 is used for better coverage.
This map can be used to check if your area has 5G coverage. "5G platus" refers to band 28, while "5G greitas" refers to band 78.
As for the antennas, if coverage in your area is good, the included antennas will be just fine, however, if the coverage is spotty, we recommend checking out our partner Poynting. We also have a Wiki article regarding third-party antennas.
Hope this clears it up!