That's known as a "signing table". Trump himself has used it before in 2017, and even joked about it himself. Or at least the audience laughed at his comments.
While the seal seems to be a more recent addition, there's a very similarly looking table being used by Reagan... well, to actually sign documents.
President Reagan, Tom Lantos, Annette Lantos and Nina Lagergren at the signing ceremony in the Jacqueline Kennedy Garden for S.J. Resolution 65 "The Wallenberg Resolution" proclaiming Raoul Wallenberg a Swedish national to be an honorary citizen of the United States. 10/05/1981.
President Reagan signing Voting Rights Act legislation with Bob Dole, Orrin Hatch, Bob Michel, Howard Baker, George Bush, William French Smith, Joseph Biden, Charles Mathias, Melvin Bradley and Thelma Duggin in East Room. 06/29/1982.
Reagan's "virtual library" index of signing ceremonies has more photos with Reagan using it for the same purpose.
One thing I've noticed in some (if not most) of the Reagan photos is that there's nearby lectern from which to give speeches afterwards. I guess the less usual thing in the Trump setups is giving speeches and/or press interviews from that table itself.
G. W. Bush can also be seen using the table to sign a NATO accession protocol for some Eastern European countries. In that photo, the table has gained the seal.
(Video of the ceremony also shows a nearby lectern.)
Interestingly, there are actually multiple copies of that table or at least very similarly looking ones at the White House, you can see two of them being used by Trump and Liu He, side-by-side.
Bill Clinton and Obama also used them (in individual ceremonies, at least).
And also Jimmy Carter (1977):
But I could not find evidence of Nixon or LBJ using that exact table (top) design, although they did use other tables of roughly the same size for signing ceremonies. (LBJ signing Economic Opportunity Act of 1964 and Nixon signing Older American Act Amendments of 1969.)
Hat tip to Darrel Hoffman for pointing out in a comment that Gerald Ford (who became president after Nixon resigned in 1974) did use the present design of the signing table. This is at a 1976 event.
Earlier signing ceremonies of Ford, e.g. one from 1974 have him using a different design though.