So the GPS system has 31 satellites in an orbit of 20,180 km. Most of the time there are at least 3-4 satellites 'visible' (visible from a signal reception point of view) at any given moment.
The Starlink satellite constellation has many many more satellites (12,000-42,000), but at a lower orbit. To be useful there will need to be at least 1-2 visible at any given time. However there could be more.
Do we know how many Starlink satellite would be visible during normal operation?
*Normal operation as a communication system; not just as the pretty satellite trains you get for a few months after launch.