I have a network scanner on my phone. It’s off. You may take the bother of physically disconnecting it if you want, but personally I’ll keep my warranty.

Mine had an off button (key combo). Check the manual of the model before purchase. Never had to give it another thought.

Pi Hole successfully blocks all that.

Note I have my router redirecting all requests to port 53 (DNS) to the pi hole for those things that don’t obey the DHCP DNS. Not sure if Roku is one of those offenders, but I haven’t seen a Roku ad in years.