Running 1920x1080 on 32" 4K monitor will look really sharp, but it will have HUGE text and screen element sizes. Not really a good idea unless you have vision problems, and it also means you won't have much screen real estate. Running 1920x1080 is best on a 22-24" 4K monitor IMO.
For good text and screen element sizes, many people might prefer scaling a 32" to 3008x1692, but the problem with this is that the text on a 4K 32" will often appear somewhat blurry at typical desktop seating distances. This can even cause some people to have headaches, although YMMV.
After trying a 1440p 32" monitor (92 ppi), a 4K 32" monitor (137 ppi), and a 4K+ 28.2" monitor (164 ppi), I settled on the latter, mainly for the much better text quality.
My 4K+ 3840x2560 28.2" monitor has an equivalent 164 ppi pixel density to a 4K 3840x2160 27" monitor. For such a 4K 27" monitor, most people would probably run at 2560x1440 (like on the 27" 5K iMac), although I would run at 2304x1296 to get a bit bigger text. (On my 4K+ 3840x2560 monitor, it's actually 2304x1536.) However, even at 164 ppi, scaled text quality isn't perfect, although very good.
For my desktop Macs, the only one with near perfect scaling is the 5K 27" iMac (218 ppi). Personally my holy grail is a 5K 30" monitor (~200 ppi), although I'd love to have a 6K 32" monitor (218 ppi) too.
Summary, for desktop monitors (IMO):
32" 4K 137 ppi - Scaled text not so good
27" 4K 164 ppi - Scaled text very good
27" 5K 218 ppi - Scaled text excellent
32" 6K 218 ppi - Scaled text excellent