It's complicated… in a sense the bulletproof solutions are the ones that raise the cost of executing the attack above the average take. In another sense even they aren't bulletproof.

This particular attack requires getting users to sideload apps that would be rejected by the play store, and most users don't have developer mode enabled. Therefore, the cost of persuading someone to enable developer mode matters. If the procedure to enable developer mode changes from "open settings, scroll down, tap, scroll down, tap seven times" to include e.g. a 96-hour wait for developer mode to be enabled, then the cost of the attack rises by whatever it costs to stay in close contact with the victim for 96 hours, close enough to react if the victim comes close to realising the truth.

This isn't a guarantee. You can still get phished even if the phisher has to spend 96 hours in intensive contact with you. Some victims are worth that effort, maybe you are, and maybe the phisher made a mistake and puts in the effort to phish you based on the mistaken assumption that you're a millionaire.

There are also other things like that. If Google can ban the keylogger you use quicker than you can deploy new builds, for example. Still no guarantee.