Stop others from using the Roku

How obvious is it, if you don’t want the guide, you still need internet? The implication, internet is required only for 2 functions, not basic use… deeper research required.
I certainly found more the “advertising” before making my purchase too.

Sounds like you may want to get a new router.
We use a Netgear (WNDR4500v2) and comes with Parental Controls (thru Open DNS). It might work for you. At this time haven’t used/setup this feature. We have no need, yet. (Also we have a guest-network for non-residents)

A login has been requested before but for a different reason, which was to di away with pairing.