How can I write self-modifying code on Windows?

Question

When I was learning to program in assembler on a DOS system - the program could change its own code while the program was running and see it in the debugger. For some reason it doesn't work on Windows. The debugger (OllyDbg) just stops the program and writes: debugged program was unable to process exception.

I read and found such a thing as file mapping, but I do not understand if I can edit the code on the go with this and if there are other methods. As far as I understand, I cannot use the usual methods because the attributes of pages or sections do not allow me to do this?