I am really confused if masculine nouns in nominative should take the -(e)r ending or not. Or when.
This article gives examples in nominative both with and without -er ending:
Seiner Hund ist müde.
Mein Hund ist da.
This is absolutely confusing. I see no difference in case there.
I guess the same question applies for neutral nouns and -(e)s ending in nominative.
EDIT: it’s not just that website.
The “contradiction in real life” is that other adjectives do take the -er ending in nominative. I was just not sure about possessive adjectives. And could not find enough relevant examples online.