Casting to a Roku Streaming Stick+ from a phone or tablet

[CU]

How do I cast or mirror to a Roku Streaming Stick+ from an android phone or table without wifi or internet. I want to download some Netflix movies to some phones and tablets and then play them on the Roku. Seems simple enough, but so far I cannot get my phone to mirror or cast to it. Most videos I find show doing it from an iPhone or mention Samsung specifically. But, when testing from my OnePlus 6T clicking Settings/Bluetooth & device connections/cast doesn't show my Roku. Also the other phone / tablets will be of different brands. Is there not a standard way or app to download to do this?