If you embed via an iframe that you’ve inserted into a page yourself, you get one kind of content determined by your theme’s templates. If you rely on oEmbed, which is what is used when you simply provide an URL on its own line or use an embed block, you get a different sort of content.
oEmbed content can be altered through the ‘oembed_result’ filter.
I just copy the link to the post, Gutenberg coverted them automatically. I check all the code, they all use the “Embed” block, I tried to copy the link manually to the wp embeded block, the result is same. One post layout in left and right(row), others in the up and down(stack).
The embed’s internal iframe should have width and height attributes. These affect the embed content’s layout. Responsive themes alter layout based on width, narrower widths stack while wider widths might be in a row.