Eh... Forbes claims he wrote a bunch of personal checks at various press events and has actual details of which specific federal agencies the checks went to for every quarter.... up until Q3 and Q4 of 2020.
So at the very least it would appear he donated an amount of $ equal to most of his salary.... I mean assuming he didn't do something wild like cancelling the checks after the press event... but I tend to think if that happened word would've gotten out about it pretty quickly.
2017
Q1: $78,333 to the Department of Interior’s National Park Service (NPS)
Q2: $100,000 to the Department of Education
Q3: $100,000 to the Department of Health and Human Services (HHS)
Q4: $100,000 to the Department of Transportation
2018
Q1: $100,000 to the Veteran’s Administration
And so on .........
(up until 2020 Q3 and Q4 )
https://www.forbes.com/sites/adamandrzejewski/2021/02/27/president-donald-trump-probably-donated-his-entire-16m-salary-back-to-the-us-government--here-are-the-details/