There's far more power in the cheapest of cell phones (of which ALL are computers) than any DOS or CP/M computer, ever. It is what it is.
When I was a database manager way back in the '70s a buddy in the computer room called to get me over to see the incredible new memory installed on one of our PDP 1170 machines. I ran down and we both ooh'd and ahh'd as he pulled out the file drawer under the refrigerator sized computer and there before our gleaming eyes was box chock fulla 2 dozen 8"x12" sized chip filled boards ... a whopping 256k of memory. Wow! Awesome! Yes, for 1970s. Today, that amount of hard memory would take up half the real estate on a clothes fabric pin head.
So yeah, DOS and CP/M are both dead as the dodo bird. That is, unless yer only need for a computer is to write text files and play pong.

Back to the real world, yer basic choices are WinXX, AppleXX, or Linux, where each will have slight variations but each on its own proprietary hardware/software theme.
When it comes to data productivity, can Linux read/write all the WinXX Office apps? Yup. So save all yer data files, images, videos, etc to a USB drive (CD and DVD are officially now old school and near dodo bird dead - it's all flashdrive media storage) and load back on a Linux machine.
The one and only things that Linux is not great at is games and some multimedia software (high end pro audio, image, video). SO, my only need for a WinXX OS is to run a flight simulator for r/c fixed wing practice, or to help someone with a website/forum on their WinXX PC.