I think a misunderstanding there, Box 12 is for munis, VUSXX is a Money Market fund so this is related to government interest which will be part of the ordinary dividends in Box 1a.
After the 1099-DIV has been put in there is a question for "uncommon situations" which is actually pretty common these days, whether "a portion of these dividends is US Government Interest" and then you have to tell TT how much this was. That amount will then flow automatically to state returns as a subtraction to the Federal AGI
To know how much to put in, you have to multiply the dividends from this fund that are part of Box 1a, by the % provided by Vanguard either in the statement if held with Vanguard or the tax info for mutual funds on their website, see https://investor.vanguard.com/content/dam/retail/publicsite/en/documents/taxes/USGO_012025.pdf
Good news, it looks like VUSXX was 100% in 2024 but please confirm for yourself.
Not a CPA/Expert and this is my experience based on desktop software and manual input of 1099s, but I assume the same principle applies to TT Online or importing 1099s.
