Subject: Re: S&P500 valuations
Regarding Vanguard,you can purchase Treasuries on their website but not from the app.

From any account,select Transact. At the bottom of the list of instruments, select Trade bonds or CDs. You will then need to re-select the account.

On the next page select the Treasuries tab. It defaults to Secondary but I have only used the Auction option (radio button).

You will then be given a choice of issues to purchase. If there is no 'buy' link on the left the issue is not available yet.

Hope this helps.