He desinstalado VPN pero se sigue abriendo una pantalla para que lo instale

Quiero saber cómo eliminar esa publicidad

First, I’m an Avast user and not an Avast Team member.

What Avast Antivirus Program are you using ?

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I Avast Premium you can reduce these promotions:
These are a fact of the free version, but can be removed in paid versions of Avast - AvastUI > Menu > Settings > General - Personal Privacy and you can uncheck them, ‘Show offers for other Avast Products’ and ‘Show offers for 3rd party products’.

Also check the AvastUI > Menu > Settings > Notifications - Limited Mode.