Long story short, Niantic, developer behind Pokemon Go, has decided that the game will no longer support 32-bit phones with Android OS. You can read Niantic’s official statement about this move right here:

Trainers,

In an upcoming update to Pokémon GO at the beginning of August 2020, we will end support for 32-bit Android devices. By removing support for 32-bit Android devices, we will be able to streamline our development process and focus resources on supporting newer operating systems and technologies. Android users on 64-bit devices and iOS users are not affected and do not need to take any action.

If you wish to keep playing Pokemon Go, you better get yourself a newer, 64-bit phone. Unfair? Possibly. Will it help better develop the game? Probably.

We do not know when exacly will the support for the older devies cease.