The people who actually wrote the language of the 10th amendment, which was presumably someone in the 1st Congress.
The preamble originally listed the states by individual name, and the Committee on Style wasn't supposed to change the meaning of anything, just the wording.... so I'm not so sure the Preamble hasn't been used in ways that, again, wasn't originally intended. Just a thought. Obviously at this point, after centuries of legal rulings, "We the People" does refer to the people of the United States collectively, but I'm not sure that's what it was supposed to mean when written, unless Governeur Morris was being sneaky.
Well the 9th amendment reads:
The enumeration in the Constitution, of certain rights, shall not be construed to deny or disparage others retained by the people.
I'm pretty sure that applied to the entire people the Constitution applied to and not just on a State by State level. Other examples
Congress shall make no law respecting an establishment of religion, or prohibiting the free exercise thereof; or abridging the freedom of speech, or of the press; or the right of the people peaceably to assemble, and to petition the Government for a redress of grievances.
A well regulated Militia, being necessary to the security of a free State, the right of the people to keep and bear Arms, shall not be infringed.
The right of the people to be secure in their persons, houses, papers, and effects, against unreasonable searches and seizures, shall not be violated, and no Warrants shall issue, but upon probable cause, supported by Oath or affirmation, and particularly describing the place to be searched, and the persons or things to be seized.
Seems like pretty common language.
I think a better question would be, are there any examples were "the people" is used and obviously implied to mean the people of a State without clarification. I can't find any, in later on in the 17th amendment I see:
The Senate of the United States shall be composed of two Senators from each state, elected by the people thereof, for six years; and each Senator shall have one vote. The electors in each state shall have the qualifications requisite for electors of the most numerous branch of the state legislatures.
When vacancies happen in the representation of any state in the Senate, the executive authority of such state shall issue writs of election to fill such vacancies: Provided, that the legislature of any state may empower the executive thereof to make temporary appointments until the people fill the vacancies by election as the legislature may direct.
This amendment shall not be so construed as to affect the election or term of any Senator chosen before it becomes valid as part of the Constitution.
Both cases very clearly have given context of the State.
Honestly the 10th amendment seems pretty clear
The powers not delegated to the United States by the Constitution, nor prohibited by it to the states, are reserved to the states respectively, or to the people.
the powers are reserved for the "states respectively" or "to the people." I honestly don't see how any reading of "the people" cannot be applied to the people of the United States. If they wanted it to apply to the people of the States they would've either put
"the people of the states"
"the people thereof"
or of course they would have gone into a longer paragraph setting the context specifically. They specifically contrasted the "states" and "the people." I think this is very consistent with the entire message of the Constitution, of a more perfect union and any power not specifically given to the Federal government should either fall to the States or the people of the US.