For me, it mostly just depends on what I need to have done;
My regular PC: Windows, currently Win7. NEVER will I willingly install Windows 11. That POS can bite my furry calico ass.
Laptop: Depending on the specs, usually the same as my desktop if it can handle it. Though since my first ever and still only ever laptop is an old-ass Netbook, I just use it for emergency web browsing when nothing else is available, or as a surrogate SD card reader over the network using my home server sort of like a smaller Xen from half-life. I could also probably install Mint on it but I'll think about that later.
A server or other appliance: Some distro of UNIX or Linux (since BSD shares its ancestor of UNIX with Linux, though I do prefer Linux derived from Debian) depending on what it needs. Server? Openmediavault. Web server? Er.. for now I actually just use one server for everything but I'd probably just go with Mint or MAYBE raw debian because popularity be damned Ubuntu can also bite my shiny metal ass. Any other appliances, such as a network switch cobbled together with a RPi and a USB hub with multiple network adapters or some bullcrap like that... I'd just look things up or even just see if anyone else has gotten DD-WRT to run on a n RPi.
A mobile device, TV set-top box/dongle or tablet: Usually, Android/Android TV. For mobile stuff/tablet stuff I GUESS the latest iPad would also suffice but I haven't had one in years. Are they still ridiculously locked down to apple's dumb garden-in-a-wall? As for TV stuff it MOSTLY doesn't matter so long as the TV itself is "dumb" and you can just swap out the set-tip box/dongle at will. If it's got "smart" built in, I hope it's Android, or at the least Fire TV since it's just Android with orange and black clothes on with a faint smell of charcoal. As for set-top box OSes... again either Android or Fire TV, but I'll settle for other things like DiSH Hoppers/Joeys or even an old-fashioned WebTV box.