The very worst thing to do is run Win10 without adding the monthly patches. That's what was going to happen this November when Microsoft stopped shipping security fixes to Win10, but now they've delayed the cutoff for a year. This page from Microsoft explains what you'll need to do starting next month to get that extra year of security patches. Note that hacks are available online to get 3 years of updates, while new hacks are bound to be released as we get closer to the deadlines.
support.microsoft[.]com/en-us/windows/windows-10-consumer-extended-security-updates-esu-program-33e17de9-36b3-43bb-874d-6c53d2e4bf42
The reason it would be so bad to continue using Win10 without the security patches, is that every month Microsoft publishes details on the new fixes it ships, which acts as instructions on how to write malware effective against every copy of Windows without those patches. Under the hood Win10 & Win11 are Very close to the same, so writing malware based on monthly Win11 fixes is almost guaranteed to work on every unpatched copy of Win10.
As far as buying a new PC or upgrading the one you have, 6-7 years is about the right age when stuff *might* start to break. That's NOT saying anything will break -- it might last 10-15 years -- but it's old enough that if something fails you shouldn't be surprised. Or to put it another way, I'll generally replace the power supply, motherboard, fans, & AIO CPU cooler [if the PC uses one] around that time frame, depending on sale prices. But, besides our two main PCs I've also got hardware that dates back to 2009 and it's still running. You will of course get better performance with new hardware, as long as it's the same grade or better, because PCs & laptops have gotten faster -- if you currently are running something like an Intel i7 CPU and buy something with an i3 it will be slower because it's a much less powerful CPU.
That said, the choice to buy new, upgrade the desktop PC you have, or run Win11 or Linux is complicated. The Linux community is pushing environmental concerns, which are certainly valid. In the US politics can play a role, as there's a movement to not spend on anything not absolutely necessary. Tomorrow's pricing is Very uncertain given tariffs. If the economy tanks will you wish you had the money spent back in your bank account?
Personally, the logic I used was will my PC last the next 5-6 years as it is now, because there was a very real possibility of 4+ years of restricted availability & much higher prices. The motherboard was 6+ years old, but everything else was OK, so I upgraded the CPU, motherboard, & RAM during the Black Friday sales, then used my old CPU & RAM with a new motherboard building a PC for our son. As far as our older hardware goes, everything's been updated to Win11 already, with the exception of an old tablet that runs 32-bit Win10. I did the migration early so I'd have plenty of time if there were any problems.
The Vast majority of PCs, laptops, and tablets will run Win11 just fine. On lower end hardware, with a CPU comparable to an Intel i3 or lower, e.g., Intel's Atom CPUs, Win11 should provide a slight performance boot compared to Win10. [Microsoft just came out with a new set of claims that it's faster, but they're really comparing older hardware that shipped with Win10 to newer stuff that comes with Win11.] OTOH there have been all sorts of benchmarks published on higher end CPUs/hardware showing that on the same hardware there's really no performance difference between Win10 & 11. What can get iffy is if the PC/laptop/tablet uses an uncommon chipset for stuff like audio, networking, touchpad, touchscreen etc. 90% of the time the upgrade will migrate existing drivers and everything will still work, and out of that 10%, 1/2 the time you can probably find drivers to get stuff working. The only downside to running Win11 on unsupported hardware is that towards the end of 2026 if there's a new version of Win11 it *might* require an reinstall. *If* that's the case, you won't be able to upgrade via Windows Update, but will have to do it manually.
The way to install or upgrade to Win11 on unsupported hardware is to download an ISO from Microsoft, then use Rufus to stick it on a USB stick. TO install Win11 fresh you boot to that USB stick and run setup -- to upgrade you run setup from that USB stick while running Win10. If you want to eliminate most all risk, perform a disk image backup to an external drive before upgrading -- you can restore that backup to put everything back exactly as it was. Or, you can use Rufus & that ISO to create a Windows To Go drive -- a cheap SSD in a cheap USB housing works great for that drive. Boot to that drive and it'll start Win11 so you can see how it works. The downside there is that it sill not migrate existing drivers because it doesn't know they exist, though you can of course install drivers once it's running.
microsoft[.]com/en-us/software-download/windows11
rufus[.]ie