Strange I have over 100 windows pc's in service whether running
blue iris or used as home or business desktops. Dont have speed issues - all with SSD's for the OS. Windows can be just as secure as any other OS. If you are relying on your OS-any os as your only security measure then you have a problem. Linux, macos and the rest all have security vulnerabilities. It takes some self control to not immediately install every update - im sure you can do it though.
As far a paying for an OS, I buy all my systems 1-4 years old. If you were to buy a pc with no OS loaded or with linux it would likely cost MORE than one that comes preloaded with windows. More over do you have a problem buying cams made in china? What about other products made in china or other hostile nations. Do you not support macOS because apples woke policies are destroying America? Do you not buy anything from mexico or other countries that are flooding us with narcotics and illegals? I can go on and on.
Most importantly the OP was looking for software that will not run all the time. Just to configure cameras. None of your issues would be relevant. But the anti-windows folks always love to inject the hate.