This library targets .NET Framework 4.6.1, .NET 6.0, and .NET 7.0, but those are no longer supported.
I suggest updating the target framework to .NET Framework 4.6.2, .NET 8.0, or .NET 9.0.

I recently submitted #44, but if you change the TFM as described above, you can update the version of System.Text.Json to 9.0.1.