Every guide answers this with one number for the whole journey. I split it. On a three-day-old domain the first rung took hours and the second has not moved.
Google had never seen most of them. The cause was a sitemap timestamp rather than content quality, and the API I measured it with disagreed with itself between calls.
Every guide says 1200×630. Google’s Discover documentation says 1200px wide at 16:9, which is 1200×675. Both are correct, they are different numbers, and only one of them survives being cropped into the other.
Pull queries without page attribution and the two competing pages get summed into one healthy-looking row. Here are the real numbers from my site, plus the false positive that cost me a month of wrong conclusions.
The error sends you back to re-verify a site that is already verified. The actual fix is one setting in a different Search Console screen, and no guide I found names it.
There are three separate language settings and only one of them is visible to search engines. Plus the REST API call that sets it, which is not documented anywhere obvious.
Every guide says take a backup. A database dump is the wrong shape of backup if you might want to use the writing again. Here is the export I ran instead, in about twenty lines.
The usual steps get the site loading on the new domain. These are the things that were still wrong afterwards, including a canonical tag pointing at the old host and an external service depending on a URL I was about to delete.
Why the section is missing from your profile, and then the four things the REST API will and will not let you do once authentication is working. Two of them are not documented anywhere I could find.
The usual checklist covers tag placement and typos. Two causes it misses: your HTTP version redirecting somewhere else, and the fact that being verified is not the same as having API access.