So a 32'' 3840x2160 4K UHD screen, running the usual retina resolution, looks like what? 1080p?
it depends what you mean by the "usual retina" resolution (which may depend on your OS version and display) - on my 28" 4k the "Default for display" setting is native 4k (or "Looks like 3840x2160" - because it
is 3840x2160). To get "Looks like 1080p" you'll have to choose a "scaled" mode - its actually "Larger text" on mine).
At "looks like 1080p" yes, in terms of the size of menus, system text & icons, "window furniture" etc. which is gonna be a bit big on a 32" screen. In terms of definition it should be as sharp as you'll get on a 4k screen.
However, My eyes aren't wonderful but I
can use 3840x2160 - on my 28" screen - for short periods - a decade or three ago I'd probably have been fine. At 32", you might find that its perfectly OK. Bear in mind that many applications let you change the font size or zoom level for the actual content you're working on
anyway.
It all depends on (a) your eyeballs and (b) how close you prefer to sit to the screen.
If 2x (retina) is too large, and 1x is too small, just enable: "Looks like 2560x1440". This will be likely be perfect for you on a 32 inch display.
Choosing anything other than native "Looks like 3840x2160" or 2x "Looks like 1920x1080" gets you the GPU/VRAM load (which may be a problem on the Mini) and slight "softness" of non-integer scaling (which will be more noticable on a larger screen) - the dialog doesn't make that particularly clear.
The problem is that the Goldilocks-zone for display size (in terms of desk space, esp. for 2 displays) is 27" and at that size, the Goldilocks zone for "resolution" is probably "Looks like 2560x1440" which clobbers the GPU.
The long and the short of it seems to be, for a Mac Mini, unless you're planning on an eGPU, go for either a 21-24" display which fits the "looks like 1080p" mode
or a bigger-than-27" 4k display that is usable in 3840x2160 mode.