What is the best infrastructure and architecture for .NET 5?

Great replies from others here.

I know Microservices are growing not but one thing you need to be careful with Microservices is, maintainability. If your application is not being used by a big number of users, and modules don't need to run their own, from multiple data sources, you are better off using a single Web API or service. Microservices architecture is costly to develop (time, and resource) and also costly to maintain (different data source, different services etc.). Its also not good for application that are small.

All are good, focused on Microservices architecture.

But, Most Interprises don't use any of them , at the EOD these frameworks provide you a ready-made architecture with good software practices like Solid principals + Microservices+ DDD (Domain driven design) etc, which you can master with just ASP.NET Core.

So, if you have time then explore all of them but try to implement the concepts by your own with ASP.NET Core, use these readymade frameworks when you have tight timeline or you are in hurry. 

But there is no such rule that you can't use third parties framework, if they serve your need then do use them.