I'll first say that 32-bit CPUs, including x86-based ones, are not retro computing. They still carry the load of all sorts of important computing systems, today. They are still being produced (IIANM, also by Intel and AMD). Sure, with much more limited use cases, and it's definitely not the mainstream, but it's there. Not a hobby and not for a 'retro' experience.

But you are also completely ignoring limited-capabilities hardware, like embedded systems and micro-controllers. That includes newer offerings from ST Microelectronics, Espressif, Microchip Technology etc. (and even renewed 'oldies' like eZ80's which are compatible with Zilog's 8-bit Z80 from the 1970s - still used in products sold to consumers today). The larger ones are quite capable pieces of hardware, and I would not be surprised if some of them use Debian-based OS distributions.