Have two versions of Xorg at the same time and choose between them in grub

I have a very old PC, The nvidia driver is deprecated, And it needs to downgrade Xorg to 1.19.xx and kernel to 5.4.xx

However, Except for OpenGL and WebGL, Nouveau driver works fine and lets me to use the latest Xorg and kernel, Switching between nouveau and nvidia drivers using modeprob options is easy enough

But how can I have two versions of X server and choose between them?

I guess it can be done by installing Xorg 1.19 in a different location and use init scripts to start it instead of the X server

Thanks very much