To be clear, this example, where the singular they is used for a person of any gender, is confusing to you.
Example of current use:
Bob - “Hey Jo, Frank thinks we should tweak widget X.”
Me - “Yeah well, they don’t know what the fuck they’re talking about.”
Is Frank part of some larger group that doesn’t know what they’re talking about? Or is it only Frank that doesn’t know what he’s talking about?
Based on the above questions, the confusion is about attempting to identify if the singular they or plural they is being used.
But these variants with a person with an ungendered name or description are fine. Example with ungendered name:
Bob - “Hey Jo, Kelly thinks we should tweak widget X.”
Me - “Yeah well, they don’t know what the fuck they’re talking about.”
Example with ungendered description:
Bob - “Hey Jo, the engineer thinks we should tweak widget X.”
Me - “Yeah well, they don’t know what the fuck they’re talking about.”
If that is true, that the second and third examples are not confusing, then determining whether the singular they or the plural they is being used is not the source of the confusion. As in all three examples, we have a person who was previously referenced excluding the possibility of the plural they. In the first example Frank, in the second Kelly, and the third the engineer. All that has changed in the first example is that the singular they has no restrictions based on name or description. If that grammatical distinction is the source of the confusion, so be it, but let’s be clear on what the confusion is.