It’s more than you think. I work with the MSP430 microcontroller, which is capable of a sleep current of 40nA @ 2V, full active mode at 140uA/MHz with all onboard peripherals turned on. With this you could achieve almost a 20% on-off ratio with a 1MHz clock, or keep it in active mode all the time at ~150kHz, which is sufficient for many embedded sensor applications.
The buggest hurdle is usually software. Make a list of all the applications you use on a daily basis. If they all have a linux version that’s great, otherwise I’d suggest finding alternatives that work on linux (or at least work okay through WINE) before you switch your OS. Ideally you would swap out all your software for linux-compatible ones before you even switch away from Windows to get a feel for everything and minimise the amount of things you have to learn all at once.
After that choosing a linux distro is honestly not as life-defining as you’d think. Don’t feel like you have to stick with the first distro you choose, as chances are you won’t pick the right one for you until you know a little more. I’d recommend setting up a USB drive with Ventoy and filling it full of distro images so you can get a feel for how they work without too much fuss.
For reference, my personal journey started with Ubuntu, then Kubuntu (uses the KDE desktop which I much prefer, instead of GNOME), then I hopped over to Arch-based distros with Manjaro (finally got me away from the very clunky and annoying PPA system that Ubuntu and derivatives have), then EndeavourOS when I realised Manjaro is honestly just a hot mess (the devs have screwed up several times. A more vanilla Arch distro like EndeavourOS works way better for the AUR too).
How has nobody recommended Supreme Commander (Forged Alliance)? It’s the inspiration for other games in this thread like Planetary Annihilation and Beyond All Reason. It’s so good that when the official servers shut down the community banded together and formed their own server and dev team to continue regular balancing and updates. It’s on steam and works on Linux with minimal tinkering. You can either play the campaign on the Steam version or head straight over to Forged Alliance Forever, the community-hosted server, to access the campaign (with added multiplayer support!), all the new patches and mods, and play some multiplayer games too.
The MSP430 is just the chip I happen to use at work, if you’re not convinced you could try looking for an actual ultra low power chip, I found the STM32U0 at 70uA/MHz and the STM32U5 at 16uA/MHz in the first result.
Even ignoring selecting a more efficient micro, a smattering of tiny ceramic caps will buy you a few hundred microjoules for bursts. If you’re already operating at 2V you can get a 6V rated 100uF cap in a 1210 package - and that’s after considering the capacitance drop with DC biasing. Each one of those would buy you 200 microjoules, even just one ought to be plenty to wake up for a few tens of milliseconds every second to get a reading from some onboard peripheral (as an example) then go to sleep again.
For sure, you’re not going to be doing any heavy lifting and external peripherals could be tricky, but there are certainly embedded sensor use cases where this could be sufficient.