macOS has had free upgrades since OS X Mavericks in 2013. Yea we can squirrel around the specificity of this (e.g. is it really free if you have to pay $99 to update Parallels?) but in pragmatic terms the actual OS has largely been free for consumer use.
I generally get the idea being communicated, but its content is so out of date at this point.
All cool on GNU/Linux until the latest kernel breaks something or the driver package that you have installed drops support for your GPU because fuck you.