It does not matter if you have the "app" or not to be tracked and "watched" as far as covid or anything else. They have the databases of who is who and uses what phone. They have the CONSTANT feed of what phones (tracked by IMEI, ESN, MRN, SIM...) are where at any given time (and THEY keep a minute by minute log of all of it so that they can go back and track at any time). They don't need any "app" on your phone, they just need your phone to be on one of their networks. The "app" only lets YOU know if you are either close to someone being watched, OR if you are being watched (and maybe not then).
And everyone that has a flip phone, or one of the older non-iOS and non-android, you are being watched as well since the system does not need an OS to track you, just a, IMEI, ESN, MRN, or SIM.
And since a LOT (read most) of the service providers have gone VoLTE or similar, they now have access to the packetized data from any source on your phone. Before they did not have legal access to the voice, since it was an actual voice channel by itself, and protected at least somewhat by eavesdropping laws. Now all of the voice data (both directions) is translated into packets and sent across the same data channel as the rest of the data streams so that they legally can do whatever they want monitoring it. And I'm not talking about TPTB, I'm talking about corporations themselves, which don't have the same restrictions as TPTB in the GOVT. So think about all of the data mining that is going on with your voice calls that has been going on with the rest of your data for decades...
Loup