Issues with Iowan Old Style Font (purchased version)

The OS can't display it because your purchased font conflicts with the OS installed copy. Or said another way, it has the same internal names, so the OS hides it the same way it does the included copy.

Despite the fact you can't see the OS copy listed in your apps, that doesn't mean it isn't active. They're all active, but those not meant for your region or language are hidden. Some apps purposely ignore this division, like all of the Adobe apps, the SoftMaker Office suite and Master PDF Editor. But most have incorporated Apple's API to hide the same fonts the OS and Apple's supplied apps do. Such as the Affinity suite.

You cannot remove or disable the OS installed version. Your only option is to change the internal names of the font you purchased. But doing that would likely fall under a copyright violation (modifying the font without permission).

Here's what you'd be looking for. This shot is from FontLab 8. While this is the Roman (normal) font in the OS supplied copy, it's pretty much a given your purchased copy has the same internal names.

There are seven faces in the set, so they'd all have to be changed.

One way would be to use the free, open source font editor, FontForge. But again, you'd very likely be running afoul of copyright law. Better would be to contact the owner of the font and see if they'd be willing to send you an updated version with new internal names.

I'm just surprised the system cannot tell the difference between font files that were installed at a later date.

Font type or age has no bearing on what the system sees. It's all, and only, based on the internal names. You can have an old Type 1 PostScript font, and a brand new OpenType font that was given the same internal names as the T1 PS font, and you'll have the exact same problem.

While I get the idea behind Apple's decision (this started back in El Capitan), it's also as major disruption for advertising agencies and publishing. You can't get at fonts you need to work on a project, and now since Ventura, you can't even disable conflicting fonts installed with the OS.

I'd guess it's the entire reason Adobe won't implement the API. You see all of the OS fonts in their lists. Including ones you'd rather not have to constantly scroll past, like the 100+ Noto Sans fonts.