Yes, not all modems have Linux drivers and not all of them has drives in Turris OS. In that Czech section of community documentation are some modems specified but those are connected trough usb.
I would suggest using the one we shipped as part of indiegogo campaign as that one is already tested. You can conveniently see everything that was in package for example in this topic: [SELL] unused Lte modem EU for Turris Omnia / [PRODEJ] nepouzity Lte modem EU pro Turris Omnia.
You can look here on forum for other test results. I know that some users were trying other modems too but I can’t suggest any such modem because I wasn’t tracking any of those tests.