Based on YouTube's robots.txt file, the Sitemap used by YouTube is an XML Sitemap. This may not be the only sitemap they use, but the one they list in their robots.txt file.
Note that the sitemap points to the "yt" subdirectory. This subdirectory is a gateway to other YouTube sites such as "YouTube for Developers" and "YouTube Advert" (which has its own sitemap without style). They do not even bother to list the usual website that is so popular and so widely shared. Honestly, unless there is a larger strategy, the site plan seems a little random. Maybe they have not maintained it for a while.
An XML sitemap does not mean that everything it contains will be permanently indexed (it depends on the search engines). It does not mean that anything that is not there will not be indexed. It is suggested to search engines to pay special attention to certain folders and files.
Based on the above, if you create an XML Sitemap, place it at the root (or near the root, in an accessible folder), then list the most important pages (homepage). , category pages, etc.) followed by search engines. and index the contents of these folders (individual videos, publications, etc.). Just make sure that these contents are not unindexed / tracked elsewhere in your settings and that the XML Sitemap (or more, depending on your structure and strategy) should suffice.