Why and how is this protecting against a malicious actors? You can't skip that part.
What about malicious actors that are entrenched, like Meta and even Google? Does this not strengthen them?
I can't say whether the specific implementation will be an improvement, but that is clearly the intent.
Meta and Google have not shown themselves to be "malicious" in sense that is relevant to this discussions. Whatever shady practices they may or may not have is very likely entirely within the law, and they are strongly motivated to protect people's personal data, because they will not have users (i.e., their product) if their platforms are insecure.
The only reason, and it is the only reason, you do not view Meta as a malicious actor is because they've told you many times they are not.
Most Meta and Google products could be described as keyloggers or spyware. Many break permissions expectations - for example, Google apps have special privileges that allow them to circumvent some permissions on Android.
In addition, both Meta and Google products are primarily ad driven, with the majority of ads being scams. Again, virtually identical to other malicious apps.
Is any of this legal? Maybe, maybe not, you signed a EULA. But if all it takes is a EULA, then most android malware is not malware, and we're back at square one: play protect will not do anything.
And, to be clear, this is intentional. It is not Googles intention to squander malware because they rely on malware. No malware on Android and they go bankrupt.
It is their intention to further extract value out of the Google play store by leveraging their mandatory 30% cut. As well as making Android a more locked down platform and thereby more attractive to advertisers and DRM distributors.
The only difference between a malicious app exfilitrating your cookies through an exploit and Meta exfilitrating your cookies through an exploit is you trust Meta won't use your cookies to impersonate you, steal your browser sessions, drain your bank account, etc.
But that's just pure trust. Meta could easily have a leak - Experian had a leak and people lost millions of dollars.