The first one my family owned, was Windows 95.

Not sure if the first one I used was Windows 3.x, DOS, or MacOS

First OS was DOS, though my parents used a computer with Windows 3.1 on it before we got the dos box.

Excluding Damn Small Linux, first real Linux was Mandrake 9.2 (download edition).

Of course Ubuntu was my first Linux distribution. I didn't use it for long.

First OS: DOS 4.something on dad's PCXT clone.

First Linux: Kurumin Linux

The first OS I recall using is Windows 7 (yes I’m young), and for Linux, I switched from Windows 11 to Linux Mint, which is what I use in the present day.

First OS: I think it was Windows 98. I have then gone through XP, Vista, 7 and staying at 10 for as long as i can.

First Linux distro: Ubuntu 10.04 or 10.10 don't remember clearly but it certainly was before GNOME 3 and in a VM. From then i have also run Fedora, Debian and most recently Linux Mint and Pop! OS in VMs as well. Maybe one day i finally set up a dual boot...

mint->chromeOs->kali->windows->arch->openbsd->arch->nix

Red Hat 7