my iMac (updated) will not develop raw files from my new new omd1 e-m1iii. will this change any time soon???

Is this Olympus OMD E-M 1 III a new model of camera.

Apple does not update its RAW database for cameras in older OS's it only

keeps the latest OS (Catalina) updated with new Camera RAW profiles.

Read through the articles below and see if your camera makes an appearance.

Digital camera RAW formats supported by iOS 11 and macOS High Sierra - Apple Support

Digital camera RAW formats supported by iOS 12 and macOS Mojave - Apple Support

Digital camera RAW formats supported by iOS 13, iPadOS 13 and macOS Catalina – Apple Support

From a quick glance I don't think it is supported in Catalina yet.

You may be able to download the free Adobe DNG Converter, this will convert your Olympus

RAW files to Adobes .dng file which you can then open and view in Preview and Photos plus other

image processors/ editors.

https://supportdownloads.adobe.com/detail.jsp?ftpID=6955

The Adobe DNG converter will operate on macOS High Sierra and newer,

what OS are you using, you have posted in the High Sierra community, but your profile says

10.12 (Sierra).

Just to add, I wouldn't expect your camera to be supported before macOS 10.16, if then.