The answer is here (under “DbContext pooling”): https://learn.microsoft.com/en-us/ef/core/what-is-new/ef-core-2.0#dbcontext-pooling
DbContext is not thread-safe. So you cannot reuse the same DbContext object for multiple queries at the same time (weird things happen). The usual solution for this has been to just create a new DbContext object each time you need one. That’s what AddDbContext does.
However, there is nothing wrong with reusing a DbContext object after a previous query has already completed. That’s what AddDbContextPool does. It keeps multiple DbContext objects alive and gives you an unused one rather than creating a new one each time.
Which one you use is up to you. Both will work. Pooling has some performance gains. However the documentation warns that if you use any private properties in your DbContext class that should not be shared between queries, then you should not use it. I imagine that’s pretty rare though, so pooling should be appropriate in most cases.