I use an appletv. I have the version with a Ethernet port. It plays everything I’ve thrown at it so far and don’t have to endure commercials. The downside is you have to create an Apple account to install apps on it and not all apps are available. It’s also expensive.

You could buy a pfsense capable mini-pc ~$200. It will give you, 1 wan port and 2 or 3 lan ports or repurpose an old desktop by updating it with a dual network card. The pfsense mini pc will use a lot less power long term. Then use your routers in access point mode, one for your IOT on 2.4ghz and one on 5ghz for the other stuff. You can set up the firewall to prevent the iot network on the second lan from seeing anything on the primary lan but still have full access to devices from the primary to the IOT network.

Easier solution is what was already suggested is by using vlans with one router and the setup the second router in access point mode for the IOT