Stocks Alphabet Owns

I wasn’t aware Alphabet has an investment portfolio; it’s been in the financial news recently because of its trade in Robinhood.

I looked at Alphabet IR, the annual report, etc., but cannot find a listing of what stocks the company owns. Is there a page on the IR site that lists this, or a page number on the annual report? Does Alphabet have to report positions monthly, or quarterly? I know there is that 13F requirement (or whatever the number is) but I don’t usually keep track of those filings closely…mostly hear about them whenever headlines about Buffet moves start to appear. Thanks…