I have an old android tablet (and several phones) that I want to use for small applications in my home automation.
For the most part just to show a web page to quickly click something to activate or read the status.

My issue is the OS installed is very old and of course there are no official updates.
Looking for custom roms they are also somewhat old because the age of the devices, and everyone says “don’t use the rom of one device into another even if the models are very similar”.

So, my question is, what are my options if I can’t use a pre-built rom?
Could I keep the same OS and just restrict access to only my internal network?
Not sure if I’m being too paranoid about security risks using these devices to just connect to my services.