TLS 1.2 - unable to run .NET 5 WebApi clean template (Windows 7 + VS 2019)

Question

I've been struggling with it the second day. I created a .NET 5.0 WebApi template in Visual Studio 2019 (simplest WhetherForecast). When I run the solution, the browser opens and I get the message (Firefox browser):

The machine I tried to run it on has Windows 7 (SP1) installed, and based on what I read, it should still support .NET 5. However I think the problem is with some internet configuration itself, because when I go to about:config in Firefox, and change the setting security.tls.version.min from 3 (TLS 1.2) to 1 (TLS 1.0) then it opens fine. I already tried:

• removing local certificates and repairing IIS Express 10
• following the guide to enable TLS 1.2 on Win7: https://manage.accuwebhosting.com/knowledgebase/3008/how-do-i-enable-tls-1-2-on-windows-7.html

but without any luck.

I could of course switch to TLS 1.0, and Win7 setup is just temporary, but I'm curious what's the cause of this error. Any ideas?

Thanks!