
After some digging and conferring with colleagues, it appears that this is indeed related to the Monaco SQL Editor.
The MSysSQLComments table is created
- When the Monaco SQL editor is enabled in an accdb
AND - When you first save a query in that accdb, with or without comments in that query's SQL.
Later, when you export a query from that Monaco-enabled accdb or copy/paste it into an accdb with Monaco SQL editor disabled, the MSysSQLComments table in the target accdb is not available and isn't created because it's not Monaco enabled.
That's the source of the error message.
On the plus side, the query is successfully exported and runs as expected inasmuch as the comments table is not relevant in that accdb.
I think the error message should not be displayed in this scenario, although it is technically accurate.
If an error message needs to be displayed to indicate that comments on SQL made in the Monaco SQL editor will be lost when exporting to a non-Monaco-enabled accdb, that would be appropriate.
In short, it's an inappropriately worded warning IMO.