The simple but disappointing answer is that if you want a guaranteed level of functionality, you need to be looking at the Thunderbolt branding and ignore almost all the USB nomenclature. IIRC, the inability of some Apple Silicon machines to drive multiple external displays is why they're only advertised as "Thunderbolt" rather than TB3, 4 or 5: the specs are strict enough that even Apple can't cut corners without consequences.
I don't think this is true. If you look at the M4 MacBook Pro spec pages, it says Thunderbolt 4 for the base model, and Thunderbolt 5 for the M4 Pro models...
The ones listed as "Thunderbolt / USB 4" ie. not Thunderbolt 3, 4 or 5, appear to be exactly the models that are limited to one external display (I'm not 100% sure about the iMacs). The models you mention with M4 and M4 Pro are all capable of driving multiple external displays, and the difference between TB4 and TB5 for those models is one of the maximum data rate (40Gb/s vs 80Gb/s with an asymmetrical 120Gb/s mode).
But I've never actually read a Thunderbolt spec, so I can't be sure exactly what disqualifies those "Thunderbolt / USB 4" from being advertised with a more recent Thunderbolt version number.
