Anything older than a Pentium II/III based on the 440-series platform is "supported" not "Supported (green checkmark emoji)".
On an actual, physical i486 systems, you run into so many problems that it is unusable.
Even on embedded systems where a 486 core was thrown into a SoC and "modern" I/O was bolted on you often spend more time troubleshooting problems than you would spend moving the entire product to a newer architecture.
Most of Linux worked, to it's credit, though I needed to tweak libata for some IDE controller quirks presumably lost in the PATA driver transition in 2.6.20. VTs worked fine and KMSCON worked well, once I loaded the radeonfb driver in initrd.
Where it noticibly falls apart is trying to being up X11, as the driver stack in X11 and Mesa have bitrotten (and in Mesa's case, removed, and no one is looking at mesa-amber from what I understand). A lightweight tiling manager and urxvt was enough for it to crash the whole system.
In any case, X worked reasonably well; 31 fps in glxgears with llvmpipe. Still a bit too slow for something like alacritty, but at least using herbstluftwm wasn't painful.