Let's say I submit a sitemap page that contains all the links I want Google to crawl, but instead of submitting a sitemap, I fetch the page and linked pages and let Google index them. How many levels of sub-pages do those bots crawl to? Do they crawl chain-linked pages or do they only crawl the links on the fetched parent sitemap page?
The "old" GSC does state:
Crawl this URL and its direct links
So, that would be just 1-level deep.
The "URL Inspection tool" in the "new" GSC doesn't appear to give you a similar option and only crawls a single URL as far as I can tell.
On my sites, I have an XML sitemap but I only include "real content" in it (so on WordPress, I include
pages, but not
categories) and I have an HTML sitemap that I code by hand so I have total control over what links are on it and anchor text of those links.
Those sitemaps combined with my navigation and internal linking within the content have always been enough to get the "real content" on my sites indexed but I'm not sure any of my sitemaps have had every URL I submitted indexed.
I guess what I'm saying is Google crawls whatever they want to and sitemaps are just hints to the crawler. Even using Search Console to fetch pages is no guarantee Google will include them in the index of your site.
If you have good content that you want Google to notice, the best way to do that is probably by ensuring there are external links to that content, which could be as simple as sharing the URL on Twitter or using Feedburner.