With the built in System.Text.Json serializer, serializing objects to and from JSON in .NET is FAST! However, the actual performance you get depends a bit on how you use it. Using DotNetBenchmark, we take a look at some different patterns that can be used for serializing an object to and from a file on disk.
Benchmarking in .NET: https://benchmarkdotnet.org/articles/overview.html
JSON Serialization: https://docs.microsoft.com/en-us/dotnet/standard/serialization/system-text-json-how-to?pivots=dotnet-6-0