The new trend of: You consent to advertising or you pay

Hi, lately I have come across a new trend which I am not a friend of.

Some of previously free apps are now forcing me to either allow personalised advertisement or else pay for the app.

My question is, is it even legal or within Google Play / Developer policy that developers can force user into consent or payment on FREE apps?
Imho forcing someone to make payment on free app to even function is against some policies surely.

I …

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