I have a few public facing AGOL applications which I've wrote over the past few months. For no obvious reason (*), none of them work now because my account seems to no longer have permissions to creates hosted feature layers. Layers I previously created still show up as content but post a "Error previewing layer / Layer preview no supported for secured feature services.". Like this:

The organizational account I'm using has Admin privs:

According to the documentation, (and consistent with my recollection of what I actually did some months ago), to create Feature Layer I should:
1) Create a new feature layer in ArcGIS Online.
Login to your ArcGIS Online account, and in the My Content section, you can click the Create Layer button to create a new hosted feature layer.
However, I don't have a "Create Layer" button there. Instead, here's what I get when I got to My Content / New item (+):

No "Feature Layer" here. Why not?
(*) One suspect is that I recently installed the "Tree Management Solution". It's was not what we need and I uninstalled it.