Internet security is easy. Unless you are specifically engaged on the internet pull the cable or shut off the network card.
I have one computer I use for internet only and another where I keep my data which has no internet capability. It’s easy enough to port with a usb stick. Computers are cheap enough to have a couple.
Or use a netgear usb wireless device and pull it out of the slot when you aren’t online. Problem solved.
Bingo.... virtual OS is also something to consider.