Ask HN: Any aggregated banking service since FDIC protects only $250k

Yep, this exists. Look for IntraFI or MaxSafe.

In more detail in this article: https://www.nerdwallet.com/article/banking/how-to-insure-you...

Besides what nvader mentioned, a government money market fund from a big managers such as Vanguard or Fidelity should be safe. You can also buy Treasury bills and bonds directly from the government through TreasuryDirect.

Back when Merrill Lynch was a full-service broker and CDs paid enough interest that you'd care, your broker could look up CDs offered by various banks and also a secondary market of CDs that people wanted to sell and you could invest money FDIC insured that way.