Well, you CAN embed X3 into another website using IFRAME, but it's not elegant. You will get the entire website, and can't just choose what parts of the website to include. You could use some custom CSS to HIDE certain elements on the page so that it looks slightly better when embedded with iframe, but it's still a clumsy solution, and the website will have a scrollbar inside the iframe. Unfortunately, it's just not easy or elegant to embed one website into another, because you have to use iframe and that simply adds the entire website inside a limited area.
I actually built a separate gallery app specifically to "embed" galleries into other websites without using IFRAME. It's much more elegant, but it's not X3 related, and does require some technical setup:
https://embed.photo.gallery/