I had a look and can’t see which isn’t centered. In general embeds are an issue. If they have specific width & height, you need a column of equal width that you can then center on page.
You can try putting your embeds within a group that has a custom class specified. Then target the group with some custom CSS that centers the content in the group. I prefer flexbox, so it would look like this:
.my-custom-group-class {
display: flex;
flex-direction: row;
justify-content: center;
}
I tested this on the “Destiny 2: The Edge of Fate – What is Kepler?” YouTube embed on the page you linked and it works – looks like you already have the embed within a group as well, so you just need to add a class to the group and use the CSS above.