Did you try looking through the modifications at all? I found this -
https://vborg.vbsupport.ru/showthrea...highlight=new* - I'm not sure if it's what you want.
Writing a query like that is not necessarily easy. I wrote my own for my site, but did away with all permissions issues because I didn't need any. The regular showthread query is full of permissions issues. You need to figure out exactly what you want and whether permissions come into play at all.