The two main problems I ran into were 1) software support at the application layer, and 2) video driver support. There is a herculean effort on the part of package maintainers to build software for distros, and no one has been building 32 bit version of software for years, even if it is possible to build from source. There is only a very limited set of software you can use, even CLI software because so many things are built with 64 bit dependencies. Secondly, old video card drivers are being dropped from the kernel. This means all you have is basic VGA "safe-mode" level support, which isn't even fast enough to play an MPEG2. My final try was to install Debian 5, which was period correct and had support for my hardware, but the live CDs of the the time were not hybrid so the ISO could not boot from USB. I didn't have a burner so I finally gave up.
So I think these types of projects are fun for a proof of concept, but unfortunately are never going to give life to old computers.
That seems odd? Debian 12 Bullseye (oldstable) has fully supported i386 port. I would expect it to run reasonably well on late 32 bit era systems (Pentium4/AthlonXP)
But otherwise, yes, Debian 12 should work fine as you say. Not so long ago I installed it on an old Pentium M laptop I had lying around. Did take some tweaking, turned out that the wifi card didn't support WPA2/3 mixed mode which I had configured on my AP, so I had to downgrade security for the experiment. But video was hopeless, it couldn't even play 144p videos on youtube without stuttering. Maybe the video card (some Intel thing, used the i915 driver) didn't have HW decoding for whatever video encoder youtube uses nowadays (AV1?), or whatever.
The CPU will be struggling with most modern video formats including h.264.