how can Linux be a moderated product to sell for desktop

It kinda depends on each individuals' use case; there's lots of different Linux distributions that are better (or worse) for specific workloads.

Any given laptop I'm staring at in a store will probably work perfectly fine as a general-use machine with Linux Mint installed. This is my go-to distro when repurposing a machine because it works great out of the box. If I were running a computer store and wanted to sell consumer laptops with Linux on them, I'd default to Mint.

If someone is looking to turn their PC into something more specialized for gaming, they can look at something like Bazzite or Batocera. These will generally require some tinkering.

If an individual or company is looking to build an office with many workstations and user accounts, they might consider Red Hat Enterprise Linux so they can benefit from official support channels if something needs troubleshooting. Many computer labs at NCSU used RHEL when I attended many years ago.

Want a stable server environment? Debian is a standard pick.

Want a barebones system with no bells and whistles (but great battery life)? Alpine oughta work.

So Linux has many options for end users to pick from, which can be seen as a good thing (more options is generally good), but also a bad thing (many end users might consider the plethora of options to be overwhelming if they've never used Linux before).

Linux (or is called unix?)

Linux (Or GNU/Linux) operating systems are a modern implementation of an old research OS that was called "Unix". Spiritual successors to Unix like Linux and BSD try to bring a lot of the design philosophies of Unix into modern OSes (I believe this is generally called the "POSIX" standard. e.g.: macOS is a POSIX compliant OS, iirc).

If I've gotten any of this information incorrect, please don't tell Richard Stallman.