which one is best suited for gaming? I do a couple other things as well but I would expect that any OS could deal with those. I know vaguely about proton / the steam deck improvements that trickled down, but don’t know if and how that affects different Linux versions.

Recommendation answer: I'd probably start with Pop! OS. It's a good starter distro with a lot of very useful things configured nicely for new users out of the box.

Useful knowledge answer: Most distros are identical for gaming. Steam can be installed on basically any of them. As long as your graphics drivers are correctly setup on whatever you choose, you're fine.

I read some days ago that ubuntu is being used by Microsoft, does that mean it is more compatible with their other applications?

Nope. Microsoft apps aren't purposefully written to be compatible with Linux at all - If WINE (windows compatibility layer, also used by proton) can run it, it'll run on any Linux distro. Microsoft is just using Ubuntu for WSL (Windows Subsystem for Linux, a developer tool) and their cloud servers.

I also read that amd is better suited to linux because nvidia refuses to support it, which would be a happy coincidence for me because I just recently built a fully amd computer, is that actually true?

Nvidia works fine on Linux - I run an RTX 3080 with no problems. The main reason AMD is considered better is that AMD's graphics drivers are open sourced, meaning they are generally better-maintained and yes, better-supported by the company specifically. In other words: You're less likely to have problems on AMD, but Nvidia works fine if you have it.

And lastly, provided there is even a definitive answer to my first question, where should I look to get started? I have never dealt with Linux before but would consider myself reasonably tech / computer savvy.

Linux can do something that Windows cannot: "Live boot" environments. That's a fancy name for "the installer runs within a functional, read-only installation of the OS". You can download things, install applications, poke at stuff, etc. but your changes are only stored temporarily in RAM, and don't actually change the boot media.

As such, the easiest thing to do to get started would be these steps:

1. Get Ventoy. This will let you boot to Linux installation+live media by just copying ISO files to a USB drive.
2. Install Ventoy on a USB drive of your choice (bigger is better)
3. Download a few distribution ISOs - I recommend downloading the ISO for each of these distros: Pop! OS, Linux Mint, Manjaro, and Nobara.
4. Copy the ISOs to your Ventoy drive
5. Boot your computer from the Ventoy drive (many will do so automatically), and choose one of the ISOs you downloaded.

Bam! You're in a Linux environment. If you wind up wanting to install it, there's an icon on the desktop of each of those distros for doing exactly that. Most will even walk you through the process of dual-booting.

Caveat: if you dual-boot, the bootloader installed by Linux will become responsible for the boot process - So your Windows installation can/could still be broken by it if something goes wrong during installation. Make sure to create a known-good backup first =]