System.Text.Json routinely fails to be ergonomic, it's quite inconvenient overall actually.
JSON is greedy, but System.Text.Json isn't, and falls over constantly for common use cases. I've been trying it out on new projects every new releases since .net core 2 and every time it burns me.
GitHub threads for requests for sane defaults, more greedy behavior, and better DevX/ergonomics are largely met with disdain by maintainers. Indicating that the state of System.Text.Json is unlikely to change...
I really REALLY want to use the native tooling, that's what makes .Net so productive to work in. But JSON handling & manipulation is an absolute nightmare still.
Would not recommend.