You may want to spend some time researching the "hackintosh" community. I, too, have a 2012 Mac Pro that's running strong (hexacore, 48GB memory, 1TB NVME drive, 8GB video card). Courtesy of OpenCore (https://dortania.github.io/OpenCore-Install-Guide/) you can install new(er) versions of macOS on older hardware. I have all the security updates and don't need to update to newer hardware (albeit I did update the GPU and NVME drive, which for my purposes further extended the life of the machine).