I’m currently installing Puppy Linux on an old computer, and everything is working fine, the resolution of the boot selections were looking ok, but the moment Puppy Linux boots the GUI, this happens!!! And I tried resizing from the GRUB terminal but it doesn’t work, please help me, thank you!!
If it’s a vga monitor you could probably plug it into a modern computer to see the available video modes in the display settings. Then on the old computer just change the video mode with xrandr in your xinit