One is that after creating a new profile, when there is only one empty default deck, clicking to create a new deck will lead to the renaming of the default deck instead of creating a new one.
The other is that when there is only one deck, after I create a filtered deck, the original deck does not appear, as shown in the screenshot below.
I think what you’re seeing are 2 expected behaviors of the “Default” deck.
It’s not quite that.
Anki starts with a deck called “default”; any cards which have somehow become separated from other decks will go here. Anki will hide the default deck if it contains no cards and you have added other decks. Getting Started - Anki Manual
Again, if that’s the Default deck, even if renamed, that would be expected.
Alternatively, you may rename this [default] deck and use it for other cards.