The simplest solution may be to disconnect the antenna. I would be very impressed if this negatively impacted the actual rolls-down-the-road functionality, since it's always possible that a car is in an area that has no cell service, and it would need to work without an always-on connection.
This is unlikely to be in the service manual, though. Are people identifying where the radios in new cars are?
It's quite possible that the same antenna package providing cellular connection is also providing the antennas for GNSS and radio.
It's also not impossible that you'll start to experience odd behaviors and warnings after a month or two, as the software stack expects connectivity eventually.
All of those separate antennas are typically combined within a single antenna package in the shark fin. Doing manual placement with separate antennas is a huge pain, so e.g. BMW prefers to call Delphi and just buy the hardware to stick on the roof.
> I would be very impressed if [no cell service] negatively impacted
Tesla issued a press release years ago in which they reassured the public that their cars were used in connection-less or heavily-firewalled territories, and they still run.
While on the one hand those reassurances are sinister ("our new feature will not impair function"; "our electronic systems will not fail when driving in the desert" - which was false for some manufacturers), also note that - as one poster nearby notes - that the item seems to work properly at some point in time is not a warranty for the future.
This is unlikely to be in the service manual, though. Are people identifying where the radios in new cars are?