wrote

An analogy:

Suppose there are a group of hams who regularly QSO on VHF or UHF FM.
Although they use different rigs, all have signals with "good audio" -
clean, crisp, clear, easy to listen to and understand.

Then a newcomer shows up, with a signal that has really poor audio.
Muffled, distorted, very unclear. Not weak, off-frequency or
over-deviating,
just not clear. Varies from 'requires a careful listen' to 'completely
impossible to understand'.

Fortunately it is discovered that the problem lies in the microphone
being used by the newcomer. It's the original that came with the rig,
which is no longer made. Nothing wrong with the rig itself, it's the
mike which is the problem.

Your analogy is broken, Jim.

The newcomers microphone is analogous to Marks computer keyboard, which works
just fine.

As you well know (unless you just fell off the turnip truck) the reason for
Marks difficult-(sometimes impossible)-to-read posts is a medical condition.
Give your newcomer a medical problem (speech impediment?) and rewrite the story.
Then we'll answer your question "How should the group respond?"

73, de Hans, K0HB