I have never heard of that website you are referencing. I have not seen this mentioned anywhere else. But like all extreme leftists websites, they will confirm it as true because "someone else" says so and provide a non existent citation.
What they state cannot be confirmed:
"Donald Trump confirmed his attendance, along with Melania, in a Truth Social post"
"post" is highlighted to TruthSocial.com.
Not a link purportedly stating by Trump he confirmed he would be in attendance.
This was likely intentional. If it were true, the article would have a snapshot of the tweet by Trump. Not a generic link to TruthSocial.com