Yeah, you probably need a capture card for your HDMI to get an input.

I like the BlueAvis one for $20 (https://www.amazon.com/gp/product/B088HBRM7T?psc=1) but it's only 1080p.

you would need something like a capture card, there are some cheap ones on amazon for under 20 bucks, that you can connect to a laptop. There are several sellers that sell the same device, look around ebay, amazon, etc for the cheapest one, they look practically the same.

I dunno how hard it is to get that working on an ipad/iphone, but i know some android devices can use OTG cable to connect the same 20 bucks USB capture card to monitor using an OTG camera/view app. I use a samsung s9 sometimes as a monitor like this.

If you have another atem mini or similar device in your company, you can also use it to get the HDMI multiview on an input and to connect it with usb to a laptop to monitor it.