“You can buy them through the government website, Treasury Direct, which is an experience from the 1990s, or use the legacy brokerages like Fidelity or Charles Schwab. Those experiences are often opaque, and come with a clunky user experience. Most modern fintech apps also don’t enable you to invest in underlying fixed-income assets.”

https://techcrunch.com/2024/01/31/finvest-app-treasury-bills-fintech/