In the age of computers (GPS) do newly built airports still have the rotating beacon?
There is not a regulatory requirement for all U.S. airports to have a Rotating Beacon (unless there is federal funding requested or if certain types of operations being conducted there require specific regulatory requirements to be satisfied, e.g., Air Carrier operations, etc.)
There are some (U.S.) public airports and most (likely all) private airports that do not have rotating beacons.
If an airport has at least one lighted runway, it will usually have a rotating beacon, regardless of when it was built. Equipment is expensive to maintain over time, so if they weren’t still useful, they’d all have been removed.
Even if pilots can easily navigate to an airport via GPS, we still must acquire it visually when coming from a direction that is not sufficiently aligned with a runway to recognize the runway or approach lights. This is quite common if we’re VFR entering the traffic pattern or if we’re IFR on a circling, visual or contact approach.