I did a factory reset on my Roku several months ago and it works more or less like it would normally. Can’t set themes, which is the only big lack, but most of the important settings are still available. I know I can change the inputs and settings and stuff on it, though, because the hdmi1 is classed to PlayStation and 4 to computer.
I just did a factory reset and never connected to the internet. You can’t disconnect it from the internet without a reset, tho, or you’ll get “not connected” messages frequently, which I assume is what you are talking about.