Acer win10 64bit desktopnot eligible for win11 free upgrade . Any ideas what i can do?

Or you can install Linux on it. I would try Linux Mint. You can even test drive Linux Mint by choosing "Live" mode when booting from the Linux Mint USB installer. Performance will be poor while booted from the USB stick, but it will give you an idea of what it will be like....performance will be great once installed to the internal SSD. Plus testing Linux Mint in "Live" mode can alert you to any possible driver issues with that computer. You can also install Linux Mint to an external USB3 SSD if you want to try it out a bit before installing to the internal SSD.

Before erasing the disk, just make sure you have everything you need to reinstall Windows if you decide later on you don't like Linux Mint and want to reinstall Windows. And make sure you have a good backup of any important files stored in a format that can be accessed from any device...not just Windows so that Linux Mint can read & access those files if desired.

You may need to turn off Secure Boot in the BIOS/UEFI....I don't know if Linux Mint supports Secure Boot. You would need to check the Acer documentation for your laptop to figure out how to access the BIOS settings & specifically the Secure Boot settings.

Linux is a great way to extend the useful life of older computers, but Linux is not for everyone and it does require learning a new OS.

You do the same thing Mac owners do when the computer is too old to run the latest OS. You buy a new computer.