If you (like me) are American but not Black, you might feel like Juneteenth is a Black holiday that doesn't really apply to you. Nice to have a day off, but not really something to celebrate yourself. That's misguided.
Juneteenth is very much a Black holiday, and we should absolutely center Black people in celebrations of it. But at the same time two things are true:
A whole bunch of people were freed from a horribly oppressive institution. Everyone everywhere can celebrate that, even if the specific people who were freed have the most to celebrate. This is a historic change towards a more free & just world, and there aren't that many of those.
Like all oppressive institutions, slavery contorted & harmed the oppressors (and those who benefitted indirectly from the oppression). Certainly not to the same degree as the enslaved people, but the harm is real, perhaps most noticeably in how the poison of justifying or even just accepting one oppressive institution invites others to flourish, and also in the ways that harming others or accepting their oppression alienates us from all other humans.
So if you recognize that freedom for anyone is a victory for everyone, then there's good reason to celebrate Juneteenth whether or not your ancestors were enslaved. Again, this doesn't change the need to center Black voices in the celebration, nor does it mean we need to celebrate "America" here. But if you view African-Americans as so "other" that you can't celebrate their emancipation as a great thing for the whole world, and one that makes the world better for everyone including you, then you've got some work to do on your implicit worldview.