You can download the Windows 11 ISO from Microsoft for free. There’s a gajillon different ways to activate it for free, too. Most likely it will just activate itself, unless you built the PC.
But if you only need it to run some software, you don’t even need to activate it.
What am I dual booting if I can’t use win10 because it’s not secure, and I’m not paying for win11?
You can download the Windows 11 ISO from Microsoft for free. There’s a gajillon different ways to activate it for free, too. Most likely it will just activate itself, unless you built the PC.
But if you only need it to run some software, you don’t even need to activate it.
A pirated copy of Win 10 LTSC, since it’s the only version you should a been tunning any who.