I am forced to upgrade to Windows 11 because my SSD got completely wiped.
Do you want to keep your old Asus P9X79 and i7-3930K, or is the CPU simply too slow? This link to the Asus web site shows all the CPUs compatible with your mobo. If you cannot find a brand new CPU for sale (which I doubt) consider buying second hand. I've not been disappointed with most of my purchases on eBay.
https://www.asus.com/uk/supportonly/p9x79 pro/helpdesk_cpu/
If you still have the original ISO (archive disk image file on USB or DVD) for your old Operating System, e.g. Windows 7/8/10, Server 2008R2/2012/2016, etc., and your P9X79 was connected to the internet at any time in the past to activate Windows, then Microsoft's servers should detect your old board again after you reinstall the original OS and reactivate it automatically.
You might have to contact Microsoft's support line if you change the CPU, but keep the motherboard. If you buy an new mobo and CPU, chances are your old copy of Windows will not reactivate because you've changed too many pieces of hardware.
In other words, you're not forced to install Windows 11 just yet, if you'd prefer to carry on using the old hardware and original Operating System. N.B. Support for Windows 10 Home and Professional ostensibly ends in October 2025, unless you're prepared to pay for extended support. Most of the other versions of Windows I've listed have already expired (in terms of security updates) so perhaps a new computer and Windows 11 is the best idea.
I'm afraid that the Corsair will not fit either?
Correct. Your old Corsair RAM is obsolete. When the P9X79 was released (back in 2012?) DDR3 memory was the norm. Next came DDR4 which is still current, but the latest motherboards have been using DDR5 for several years. If you buy a new motherboard and CPU, you'll need new DDR4 or DDR5 RAM, depending on what type is required by the CPU.
3- Corsair Hydro Series H110
This might still work if it has fixings to suit the latest CPU sockets. If not, you won't be able to bolt the cooler block down on to the new CPU and motherboard. There are plenty of modern AIO and air coolers that are compatible with modern boards.
4- Corsair Enthusiast TX750M
A good PSU in its time, but if it's of 2012 or 2013 vintage, it's probably out of warranty and it might be wise to buy a brand new PSU, before the old one eventually fails. It's doubtful your PSU came with more than a 10-year warranty. It might carry on working for another year or two, but it's false economy.
6- Cooler Master COSMOS II - Full Tower - noPSU ATX
7- Asus GTX 1060
8- and a few drives
You can keep all of these parts, unless you need a faster GPU. Just make sure any new motherboard (and especially the cooler) will fit in the old case.