Disabling Internet Access While Retaining Wifi Access

I want to prevent certain cameras from connecting to the internet, but still be accessible via wifi. I'm using RBR850.

I saw on the orbi app there is an option that says "Internet Access" which you can turn on or off, however it disabled wifi access even. When I check on the router's webpage the device is added to the blocked list in access control which blocks local traffic too.

I want to disable internet access only.

I tried reserving an IP address range for these cameras and using block services set to ALL for that range, however I cannot force the cameras to use those IP addresses.

1. How can I block specific devices from internet access while retaining local-network access?

2. If that's not possible, how can I force the cameras to have a certain IP via the router?

3. If none of the above are possible, what are the best options to get what I need? Open source firmware? Hardware firewall? etc.