My suspicion is that they can only implement this law on people who actively agree with it and signed up to it, I imagine that happens when people sign the terms and agreements upon starting the chat app, otherwise a warrant and a good dose of suspicion is still needed in order to peep into people's messages.
Most proprietairy apps would then become victim to this new law, but not some FOSS-based applications like Briar, Cwtch, SimpleX and possibly even Molly-FOSS. (Signal fork)
After all, people still have constitutional rights.
Please correct me if I'm wrong.
However, considering Google might disallow such apps after Google's new policy takes place, or they will let developers sign the terms for all of their userbase instead.
I'm just speculating here though...