I am replacing an old Roku streaming player with a new one.
I want to know if, after I install all my streaming services/channels on the new player, will the watchlists from those services/channels (Netflix, BritBox, AppleTV+, etc.) still be accessible to me? Is there anything specific I need to do to preserve the watchlists so I can use them on the new player, or will I have to create all of them over again?
Those channels you mention most likely maintain things like a watchlist in the cloud, not on the device itself. Roku devices in general have very little storage space, and channels don't store such information locally. If you can check your account on a different device (such as a web browser) and you still see the same lists, then you should be fine with replacing your Roku and still having all that data available.