How do search bots index iframes?

Question

Google

When placing a code with a youtube video on a website page, for example

<iframe width="560" height="315" src="https://www.youtube.com/embed/QPC2czFDe1w" frameborder="0" allow="accelerometer; autoplay; encrypted-media; gyroscope; picture-in-picture" allowfullscreen></iframe>

When opening the page in a browser, the iframe tag will contain a canonical link to the video
. At the same time, the page itself has a canonical address https://www.missp.ru/catalog/oborudovanie-dlya-vyd...
How search robots react to the contents of the tag, in particular for the presence of the second canonical tag on the page