Update: After posting this article, I found a paper from the Army mentioning his discharge but not the discharge papers himself.
Today, this war is called World War One, but at the time, it was called the Great War or the War to End All War, a rephrase of an H G Wells book, The War That Will End War (https://archive.org/details/warthatwillendwa00welluoft/page/n3/mode/2up and audio at https://archive.org/details/the_war_that_will_end_war_1810_librivox/warthatwillendwar_01_wells_128kb.mp3).
A monument to The Great War is located at Turner Park in Omaha
In talking with a genealogist, my grandfather came up in discussion, as a newspaper article says he was a World War 1 veteran. From what I can recollect from family stories, he enlisted or tried to enlist, but by the time he did so, the war came to an end. I have found no records of his enlistment or discharge.
Finding such records can be very difficult due to the horrific erasure of history, known as entropy. The worst form of entropy is fire. From Perplexity.AI: A major fire broke out at the National Personnel Records Center (NPRC) in St. Louis, Missouri, starting shortly after midnight on July 12, 1973. The fire continued to burn for about four days, with hotspots persisting for nearly a month.
The 1973 NPRC fire was catastrophic in scale:
An estimated 16 to 18 million Official Military Personnel Files (OMPFs) were destroyed
The most severely affected were:
U.S. Army personnel records: Approximately 80% of records for those discharged between November 1, 1912, and January 1, 1960, were lost
U.S. Air Force personnel records: About 75% of records for those discharged between September 25, 1947, and January 1, 1964, were destroyed
(https://www.perplexity.ai/search/there-was-a-great-fire-in-st-l-xkFnPGaNSKOdIYAQMAJtcw)

Here is another odd thing. The United States entered the war on April 6, 1917. The draft was implemented with the Selective Service Act, which was passed by Congress on May 18, 1917. The draft began in June 1917, requiring men aged 21 to 30 to register for military service. My grandfather was slightly too young to be drafted but did he try to enlist? Unknown.
Yet, there was an amendment added to the Selective Service Act expanding the draft to include 18-year-olds, which was enacted on August 31, 1918, which meant my grandfather could be drafted but. . . the conflict ended on November 11, 1918. I suspect with the expansion of the Act, he attempted to enlist, but again, no document. He did register for the draft though around September 12 of 1918. Yet, here is his Army uniform.