Had literally half glass white wine 21 hours before ETG test, will it show?

What the heck what. What are failure consequences? No alcohol permitted?

If you are on the testing, why drink and worry about it, What the heck !

It's very possible that it will show.

Half glass wine 21 hours before ETG.. what should I expect? Can ETG stand alone in court... what are the standard across the board cutoff levels?

You should expect to FAIL.
What happens when you do should have been explained as part of the legal process.