How can I use my cellular Internet connection while streaming through Wi-Fi to an AppleTV device?

How can I use my cellular Internet connection while streaming through Wi-Fi to an AppleTV?

The reason I’m asking?

My Internet at home went out, but I still have cellular Internet. and I want to stream a program to my Apple TV.

I know in the past this was possible, but it doesn’t seem possible anymore. I know I’ve been able to use Wi-Fi without an Internet connection and use cellular data at the same time. I don’t remember the procedure and anything I look up doesn’t seem to apply.

I know this used to work. In the simple workaround, which is not that simple depending on how fast you can download a TV show. But go to cellular download the program to your iPhone turn off cellular by turning on Wi-Fi and then I can stream to the TV. But I can’t be streaming to the TV and connected to the Internet at the same time. I know I used to be able to use Wi-Fi only for local devices. Something has changed to prevent this or I haven’t figured out how to do it.

Again, this is to continue watching TV when my Internet goes down at home, but my cellular Internet is still working.