While Google Fi is understandable for your situation, for the majority of Americans who don't need international roaming, Google Fi is not the most cost-effective solution.
Mint Mobile offers unlimited plans with 35GB of unthrottled 5G and 4G data for $30/month, 12GB for $25/month, 8GB for $20/month, and 3GB for $15/month. All of these options are significantly cheaper than the same amount of data on Google Fi.
The relevant part is that Mint works just as well on phones not optimized for Google Fi as it does on phones optimized for Google Fi, eliminating vendor lock-in. Mint works on the Librem 5 and the Pinephone (and also on iPhones). Future FOSS phone hardware that uses GSM-based cell networks will be Mint-compatible.
The catch is that the rate is for annual billing, although Mint offers a 3-month trial at the annual rate.