“Windows programs are confined off-line and only Linux accesses the Net?”
The Liux will be the OS to autoload and get online with. The windows will be the secondary option from the boot (grub) menu and it will remain off line unless you boot into it and put it online.
Now you may have to make some settings in the Windows so that it DOES NOT automatically try to get online by itself when you boot into it.
Some of us are scr@#%&d because our company employer insists on real name MS accounts.
I like LinuxMint for home.
Websites that only work if latest MS is detected are a problem.