Desktops have a lot more bang-per-buck than laptops, and are significantly more repairable/upgradable. Laptops make a lot of compromises to squeeze everything into a portable form-factor that runs on batteries. However, only you can say whether that outweighs the space/portability benefits of a laptop, for your use-case.

I'm a sysadmin, I work with Linux every single day, and I say to you: do not go Linux. It isn't designed for what you want it for; it's somewhere between the hobbyist/industrial spaces, whereas you want and need something consumer-focused. Get a nice straightforward Windows box.

Macs are also decent, though they're even more bucks-per-bang than laptops, and there aren't mac versions of every application; you'd need to check what's out there.

Operating systems come with the computer if you're buying them retail; you can buy them separately if you're building from parts. Linux is free to download.

Laptops can be ergonomics hell; tiny keyboards, little screens right at desk level - if you're working at them all day, a proper monitor and keyboard are de rigeur - at which point, you may as well have a desktop, unless you need to take your computer with you when you go places.

Brands, ehh. HP and Dell are decent, but whatever. Or if you're a getting a desktop, you could build your own and save a packet, but that's a whole other rabbit hole of complexity to dive into.

You need SSD, not HDD. HDD is slow as hell, physically fragile, makes annoying grunting noises... just don't even consider it. SSD is unbelievably faster and better in every respect. A little more expensive, but worth every penny. Don't go less than 500GB, preferably 1TB.

RAM, you need 16GB at the bare minimum; consider 32GB.

Monitors: preferably 27", at least 1920x1080, consider 2560x1440 or even 4k. You don't need high refresh rate, you do want an IPS-type panel. Having two monitors will greatly improve your quality of life, if you can swing it.

CPU: there's a million and thirty different ones out there. Just get something released in the last couple of years, you'll be fine in most cases. There's usually a shoulder in the price-performance curve about 75% of the way up the rankings; that's the optimal place to buy if you want something that will keep you going a good while without getting ridiculous.