Check the manual, Mac chapters, about routing the higher mic channels to channels 1/2, then activating Loopback.

This is not complicated, it's in fact a very easy and straightforward task.
And if you need that more often then you can store this setup/routing in one of the eight snapshots in TM FX.

You ask for videos? Search with google using keywords like: RME zoom loopback
Then the 1st hit is already: https://www.youtube.com/watch?v=nyVdSTg7gII

But you also find useful information like:
https://forum.rme-audio.de/viewtopic.php?id=30723
https://www.youtube.com/watch?v=1Bca_dn7u6w

Maybe the background and the solution in a few words..
The problem is, that some application can not read audio from higher MIC channels like e.g. HW Input AN9 IN.
They can only read audio from the first stereo channel HW Input AN1/2 IN.

Activating Loopback on a HW Output Channel (klick to the wrench symbol of an output channel to see the loopback button) is like plugging a cable from that output to the corresponding input, but internally in the routing matrix, you do not need to plug a physical cable.

So all you need to do is to route the desired audio signals, best in submix mode to HW output AN1/2 OUT, where loopback is enabled so that you can either record it on HW Input  AN1/2 or that the application can access it through that input.
The routing configuration in submix mode is also easy and straightforward.
Select the HW output AN 1/2 out and then move the faders up of those audio channels, that you want to hear on that output. In this case the Mic channels HW input AN9.

The whole procedure you will see in the video, this here is only meant as a quick introduction so that its maybe easier to you to follow the video if you have already a little background.

If you think you have a reason to complain in any way as you say this appears to be like a complicated workaround, then please contact / blame the developer of such applications where it is not possible to select audio channels in a more flexible way.

Something like this would have to be provided by Apple in their audio subsystem.
I have doubts that Apple will provide such a "workaround" because in a perfect world it should not be needed.
The application should provide the possibility to select the mic input from a list of inputs on your system.

Use loopback as it is currently the only solution and be glad that RME has this implemented so nicely as it follows and easy logic and is very easy to implement and use once you understood the basics behind it. It's only a combination of two things, routing to the proper output and sending the audio stream ("submix") to the corresponding input by activating loopback on that particular output. Nothing more.

In parallel I would contact the manufacturer of such audio applications to make mic inputs selectable.
And this should be done by everybody, so that it gets proper attention / visibility.

Ok, most people might not be affected by this if they have only a computer with Mic input and speakers, not a high quality recording interface, but come on, this is no rocket science and should simply be implemented. It's ridiculous to have this issue since such a long time and that nothing changed. They should have forseen this and provide something like this from the start.

Each HW output in TM FX has it's individual submix.
First you have to select the channel "HW Output AN 1/2" in the bottom row of TM FX.
Turn the output fader to 0db.
Next you have to raise the fader of "HW Input AN 9" where your microphone is connected to.
If you do not hear something you might to set the input gain higher.
Or if you have a condenser mic you might have to enable phantom power.

Routing any HW input and SW playback channel to any of the available HW outputs and that each of the outputs has a submix of its own is the key point in TM FX design / its operation. It's not too hard to become acquainted to it.

Once you get something reasonable on the HW output, clicking the loopback button of the HW output AN1/2 to be able to record this audio on the corresponding HW input AN1/2 is no big deal (instead of having to plug a TRS cable from the output to the input on the back of your unit).

Here you can get further tips for TM FX 1st time setup and operation: https://forum.rme-audio.de/viewtopic.php?id=34394

Here two short videos which brings TM FX operation of mixer channels and routing nicely to the point in a few minutes.
The videos are from 2015, but still valid an IMHO the best as they are extremely well brought to the point:
https://www.youtube.com/watch?v=aeKpM13Eb1M (02:56)
https://www.youtube.com/watch?v=CcWClPViBm0 (03:42)