I went back, and tried the recommendation.
Took out all my NDS games from their separate folders and put them into one, on the same level as Root Directory.
I then re-downloaded the PNG GameTDB-ds_box-US-2019-07-03.ZIP file, unzipped and pasted all the PNG files into ROOT\_nds\TWiLightMenu\boxart folder.
Started up TWiLightMenu, no problems there, but still the same Red Screen error on the Top Screen.
Admittedly, I did not rename any of the 1000+ PNG files and the names of my NDS files are in the format that come as usual - GameNumber_Title_APKFixIfAny.NDS
The application can still be closed and I can still get back to my main 3DS menu just fine, so it seems to me that the whole problem is with the PNG boxart.
If there's something that I did wrong, I would appreciate the clarification.
Thank you again.
what I did was used the twilight++ updater just for box art. everything else I'd rather do manually. if you're also using a ds or something, copy and paste the box art from the 3ds into the twilight boxart folder on the slot-1 micro sd card.