I cannot delete my own folder

Using Sequoia 15.0.1 with my MacBook Air 2020 M1, I wish to delete a folder for an old project. I have copied that folder to an external disk, and now I am ready to delete that whole folder from my internal SSD drive. I tried:

Selected the folder, ⌘-delete. "Are you sure...", clicked "Delete".

-> "The operation can’t be completed because some items had to be skipped..."

Selected one item in the folder (a PDF file) , ⌘-delete. "Are you sure...", clicked "Delete".

->"The operation can’t be completed because you don’t have permission to access some of the items."

Get Info (⌘-I). "Locked" was UNchecked. Permissions are:

gil (Me) Read & Write

staff Read only

everyone Read only

Clicked on the lock icon. "Finder want to change permissions..."

Entered password. The lock opened.

Tried to change "everyone" to "Read & Write".

->"The operation can’t be completed because you don’t have the necessary permission."

Tried to change "staff" to "Read & Write".

->"The operation can’t be completed because you don’t have the necessary permission."

Tried to change "gil (Me)" to "Read only".

->"The operation can’t be completed because you don’t have the necessary permission."

This is my machine and I created that folder and the files within it. No one else should have permission to mess with my files. What do I have to do to assert my ownership and delete this old folder?

--Gil