GuardClauses | A simple package with guard clause extensions | Architecture library

I'm trying to convert milliseconds timestamp to a DateTime, but it throws an exception at reader.GetString():

System.InvalidOperationException: 'Cannot get the value of a token type 'Number' as a string.'

It means I'm trying to read it as a string when it is a value. If I replace it with reader.GetInt64() or reader.GetDouble(), it works, but the reason I'm writing that question here is because I took this class from one of dotnet's open source projects on GitHub and I doubt that I really need to change the class. I believe the problem could be in my JsonSerializerOptions.

https://pastebin.com/9AjwSp5L (Pastebin because it exceeds SO's limits)

I'm trying to implement the following API Endpoint. Due to the fact, System.Text.Json is now preferred over Newtonsoft.Json, I decided to try it. The response clearly works, but the deserialization doesn't.

https://pastebin.com/VhDw5Rsg (Pastebin because it exceeds the limits)

I pasted the response into an online converter and it used to work for a bit, but then it broke again once I put the comments.

How do I fix it? I would also like to throw an exception if it fails to deserialize it.

I keep getting this error when I try to Add Razor Pages with Entity Framework Core (CRUD):

How do I go about resolving something like this?

Here is my .csproj file

I have created a small dotnetstandard 2.1 library project in a solution. I want to test out using Nullable Reference Types. As part of this, I want to have appropriate compilation errors and warnings.

TLDR; I want to know how to setup the CA1062 code quality settings in .editorconfig correctly.

I have added the following nuget packages to the project: