David,
Thanks, Jonathan. On Debian Buster (Debian 10), the first package exists. The second wasn't found. When I tried using Synaptic, "libsdl2-ttf-2.0-0" was found. Don't know if the Setup_CodeBlocks.txt file needs to be updated?
No. It tells us which file is needed. Every flavor of Linux is different.
Tried updating the fractint.cfg file with a 256-color entry for 4K (3840x2160) resolution, but selecting it only makes XFractint SDL abruptly vanish. Yet starting with the default window size (640x480 and stock mandelbrot) I can maximize the window and XFractint happily re-renders it at 4K resolution.
A full screen resolution needs space for borders. It's an SDL thing. Although, maximizing the window, which should do the same thing, actually works. Try renaming "fractint.cfg" and starting Fractint. You should see (when you press <DEL>) a list of available video modes. I don't recall if it will get saved. Jonathan