I'm new to SharePoint on premises, now I'm in the middle of migration project SharePoint 2010 to 2019, but I'm stuck with some issues. First, I found out that I can't add AD user on SharePoint form through people picker, I couldn't find any AD user there. Later on, I found out that, user that I used and I thought site collection administrator was not it.
I checked through site settings on site collection administrator menu. I couldn't find user that currently logged in but I can access site settings panel. this is only happened on migrated site collection. I try to create new web apps, there is no problem with that, everything is fine.