Would anyone have some idea of what this error could be?

I'm a beginner in Asp.NET programming and I've been struggling with a strange error at the API... It started happening right after I upgraded Visual Studio 2019 to 16.4.0.

The problem is that I can't really understand or even find answers about it, due to its strange description. So, I was wondering if any expert out there could offer me some insight into this...

Here's a screenshot of the error

Error text:

Exception thrown at 0x00007FFB43ABA839 (KernelBase.dll) in iisexpress.exe: 0xC0000005: Access violation reading location 0x0000000000000000.

What I gathered so far:

• The error started happening only after upgrading to Visual Studio 2019 16.4.0.
• The error is thrown at the API part of the application, when the WEB part tries to connect.
• I already tried updating the framework (.NET Core from 2.2 to 3.1).
• I already tried updating all project package references to 3.1 using NuGet Package Manager.

I would really appreciate any help with this problem. I'm sorry if I left out any important piece of info. If that's the case, please let me know.