I have a router set up just for my wifi cameras. The router is not plugged into the internet, but it is directly connected to one of two Ethernet ports on my ×86 home assistant server. The other Ethernet port for Home Assistant is connected to the internet. Is there any chance a device connected that router could somehow access the internet from homeassistant?
You are bridging two networks. One that is internet isolated to one that isn’t. The danger is that some bug, exploit or even simple firewall misconfiguration allows a bad actor to gain access, exploit and do what they want.
It’s all about the level of risk you are willing to assume.