Is it even possible to completely avoid open source software nowadays though? Windows itself might not be completely open source but it has a bunch of open sour

Is it even possible to completely avoid open source software nowadays though? Windows itself might not be completely open source but it has a bunch of open source components and/or is based on open source components (even the TCP/IP stack has its roots on BSD :-P). Even your CPU (especially Intel with its IME using Minix) and UEFI might have some open source code. Perhaps if you find some 20 year old PC with an obscure proprietary operating system that has its own network stack you could do it. Though that "proprietary purity" will break down as soon as you step out of that PC box and connect it to a router or whatever since chances are it will run open source software and your purely proprietary signal will be contaminated way before reaching some end user's browser :-P