Support for Cameras

As you are posting in the macOS Mojave community then I take it that is the OS you are running.

If it is not supported in Mojave it never will, Apple does not make a new Cameras RAW files backwards

compatible with older OS's.

Apple only ever makes a new Cameras RAW files compatible with the Camera RAW file database in its newest OS,

which is Big Sur.

If you are using an older OS like Mojave and would like your mac to read your Olympus OMD-EM5 mkIII

then download the free Adobe DNG Converter. This converts your cameras RAW files to the .dng format

(Digital Negative), which can then be read by Photos, Preview, Quicklook and Finder.

https://supportdownloads.adobe.com/detail.jsp?ftpID=7053

Nobody outside Apple knows and Apple does not tell in advance. Raw updates have been recently very slow. Use Adobe DNG converter as a workaround.