There's apparently a summit organized in Egypt, where the UN chief spoke and:
The meeting, called the Summit for Peace, also included officials from Jordan, Qatar, Italy, Spain, the EU and UK. Israel, the US and Iran did not attend.
Was the US not even invited or 'uninvited'? Or did they reject the summit for other reasons?
(The summit ended without a joint statement, so I guess there's that angle to consider, that the divergences were perhaps too great to bother meeting.)
Despite the sources linked in the question stating contradictorily that "the US [...] did not attend", and that the US "only sent its Cairo charge d'affaires who did not address the meeting in public", it seems that the truth is that the Cairo charge d'affaires was sent, and that she did address the meeting hall.
Whether these remarks were made in public or not, they may be found summarised on the State Department's website here, or in full on the US Embassy website here.
I suppose the obvious follow-up question is why no high-level policy makers were sent; other invited countries sent their head of state, head of government, or minister for foreign affairs. This is not addressed in the charge d'affaires' remarks, except to note that both President Biden and Secretary Blinken "have unequivocally reaffirmed the United States’ support for a durable, lasting peace in the Middle East, built on the foundation of a two-state solution". I am unable to find an explanation from either the White House or the State Department as to why these leaders did not attend the summit.
The US was invited according to the Al-Jazeera list of countries:
Dubbed the Cairo Summit for Peace, representatives from countries including Jordan, France, Germany, Russia, China, the United Kingdom, the United States, Qatar and South Africa are attending the one-day meeting on Saturday, together with United Nations and European Union officials.
and it noted that
The absence of any representative from the Israeli side, and any senior US official, has dampened expectations for what the summit can achieve.
So it seems that they were not attended without any reason.
See also Reuters Cairo Peace Summit on Gaza conflict: who is attending?
Just to confirm with an image/video what was said in the other answers, the US indeed participated at a lower level of representation
Also, despite the existence of the transcript of a US speech (on US gov't sites), Reuters says that it was not delivered in public:
The United States, Israel's closest ally and a vital player in all past peace efforts in the region, only sent its Cairo charge d'affaires who did not address the meeting in public.
VOA confirms/repeats that level of US representation and adds that "Israel was entirely absent" from the summit.
Insofar, it's not clear [to me] why the US speech was not delivered in public.
