If anyone else has been struggling with this, I have managed to work out a solution for myself. It uses Gmail Filters, Google Sheets, and a Google Apps Script to forward emails to GQueues with proper Quick Add Syntax. It's customized from the concept/script that a Redditor posted:
https://www.reddit.com/r/ifttt/comments/b3zv1z/alternative_to_gmail_applet_using_sheetsapp/ For now, the solution I'm using is kind of for my eyes only (e.g. messy), but
if there's interest, I'll write up instructions and re-create a version of the Script + Spreadsheet specifically to share with the
GQueues community like I did for the "
Subtask Template Calculator."
Solution Overview:
1) Implement Gmail Filters to add specific Labels to emails (as they come in) that I want forwarded to GQueues.
2) Set up a Google Sheet containing the instructions/syntax for what to do with each kind of filter/label.

3) Add custom Google Apps Script to the Google Sheet. The Script will scan Gmail for desired Labels, forward them to GQueues with corresponding Quick Add Syntax, then change the Label in Gmail so the messages don't get processed a second time.
4) Set up a Trigger to run the Google Apps Script every 30 min (which is fast enough for my needs, but could be customized).