I had noncash charitable contributions in 2018, all of which appear in my TT record. Yet I saw no sign of Form 8283. Where do these contributions actually show up?

Non-cash charitable contributions are itemized deductions which show up on Schedule A of Form 1040.  You will have a form 8283 for each charity or organization that you made deductible contributions or donations to in excess of $500.    If you took the standard deduction and did not itemize, you won't find the contributions on your tax return.