I think it’s probably legally in the clear. You can have cameras at all the outside doors of an apartments complex which effectively does the same thing. And you can have fobs instead of keys.
There is more though because the app is on your phone and likely has access to more data than a key fob would provide.
And then sold.
...cameras might do the same thing, but only with considerably more effort, and due to the storage requirements of video footage, it's less likely that landlords would process the footage in time to form a simple entry/exit log. App-based fobs skips the whole processing step, and the data collection occurs on the phone, not on some device outside the owner's possession (the camera). I'd say it could be easily rejected by tenants in Europe based on GDPR, but not sure about America.