Google's John Mueller said on Twitter he doesn't believe there is a limit to the number of meta tags Google has on a per page basis. He said, as far as he knows, there is "no limit to the number of meta tags we pick up."
I assume John is referring to the meta keywords tag because Google ignores them anyway. But there can be other meta tags used, like meta descriptions, meta author, meta robots, meta viewport, meta title and so many more. So the question is a bit awkward.
Here is the conversation on Twitter:
AFAIK there's no limit to the number of meta tags we pick up, but either way, 20 seems a bit extreme :-))
— 🍌 John 🍌 (@JohnMu) September 20, 2018
So I assume Google can crawl and understand all of what is in all the meta tags but what they do with it is another thing.
Forum discussion at Twitter.
Note: This story was pre-written and scheduled to be posted now, I am currently offline for a holiday.