How can I use Apple Fitness+ on my laptop?

You need an iPhone to use Apple Fitness+. If you have a Mac you can use AirPlay. If you have a windows laptop it is possible to stream it using dodgy third party software that isn't guaranteed safe.

It's not and it's totally ridiculous I have to work out using my phone when my 3k MacBook is sitting right there.

Make Apple Fitness+ readily available on laptops and desktops. For that matter, make it available on everything. :)

Does Apple have anything like the Polar Flow...that is so convenient as all in one place and can be seen using multiple devices?