TL;DR; “Silent SMS” aren’t an actual issue in itself, just a buzzword without real world implications.
There are actually other methods to do reliable triangulation which do not necessarily involve a connection to another tower.
This is especially true for modern networks, starting with LTE.
Modems do generate measurement reports on a regular basis, in which they report their connection status. These measurement reports are usually triggered by the network when necessary, and do contain a lot of information, including the measurement of neighbor cells.
Based on this report you can actually do triangulation without a connection to multiple towers, as long as the phone can see neighbor cells.
Timings are an issue, but not an unsolved one. LTE and 5G radios are required to do phase tracking, and the required accuracy is in the microsecond range (depending on cells sizes, around 3-5 µs), so synchronization and timing is more precise than often thought.
This also shows, that “silent SMS” aren’t actually a real issue, that was just the crude GSM method to acquire status reports from mobiles; the reporting is much more sophisticated in modern networks.
It’s also not that hard to see when networks create events to acquire measurement reports - the main issue would be, that this happens all the time while the mobile is active, as measurements are crucial to LTE or 5G networks.
For anyone interested in this, many of the points are specified in 3gpp TS 36.133, which is easily available to read up.