Hi,
I am unable to remove a PPA under Authentication in Software & Updates.
Tried from terminal
$ sudo add-apt-repository --remove -y ppa:<random ppa>/ppa
No error, ppa remains.
place the flag before --remove
example:
sudo apt-add-repository -y ppa:ansible/ansible
sudo apt-add-repository -y --remove ppa:ansible/ansibleThat does not matter, i tried anyway 
but no dice 
I tried those on my system and they work fine. If you cannot add the ansible ppa, you must have some other issue.
Check out this link -
Good luck karnemelk
I found out what my problem was:
PPA’s are not shown under “Authentication”, those are PGP keys associated with the PPA’s. I still could not remove them via the GUI though. But manually i could
So i opened a terminal:
$ cd /etc/apt/sources.list.d/
$ ls -la
total 8
drwxr-xr-x 2 root root 4096 aug 1 13:03 .
drwxr-xr-x 6 root root 4096 jul 30 15:12 ..
-rw-r--r-- 1 root root 0 jul 30 15:16 gezakovacs-ubuntu-ppa-bionic.list
-rw-r--r-- 1 root root 0 jul 30 15:16 gezakovacs-ubuntu-ppa-bionic.list.save
-rw-r--r-- 1 root root 0 aug 1 17:10 mkusb-ubuntu-ppa-bionic.list
-rw-r--r-- 1 root root 0 aug 1 17:10 mkusb-ubuntu-ppa-bionic.list.save
-rw-r--r-- 1 root root 0 aug 1 13:03 teejee2008-ubuntu-ppa-bionic.list
-rw-r--r-- 1 root root 0 aug 1 13:03 teejee2008-ubuntu-ppa-bionic.list.save
$ sudo rm -rf *
[sudo] password for user:
$ ls -la
total 8
drwxr-xr-x 2 root root 4096 aug 1 19:01 .
drwxr-xr-x 6 root root 4096 jul 30 15:12 ..
Then came the brainwave
$ sudo apt-key list
/etc/apt/trusted.gpg.d/gezakovacs_ubuntu_ppa.gpg
------------------------------------------------
pub rsa1024 2009-01-21 [SC]
BCCC C1E2 8354 33FA 7DB8 5D51 D45D F2E8 FC91 AE7E
uid [ unknown] Launchpad PPA for Geza Kovacs
/etc/apt/trusted.gpg.d/mkusb_ubuntu_ppa.gpg
-------------------------------------------
pub rsa4096 2014-08-14 [SC]
29D7 6ADA 2D15 A87B F4C6 8B82 3729 8274 54B8 C8AC
uid [ unknown] Launchpad PPA for MKUSB
/etc/apt/trusted.gpg.d/teejee2008_ubuntu_ppa.gpg
------------------------------------------------
pub rsa1024 2013-01-14 [SC]
1B32 B87A BAEE 3572 18F6 B48C B5B1 16B7 2D0F 61F0
uid [ unknown] Launchpad PPA for Tony George
/etc/apt/trusted.gpg.d/ubuntu-keyring-2012-archive.gpg
------------------------------------------------------
pub rsa4096 2012-05-11 [SC]
790B C727 7767 219C 42C8 6F93 3B4F E6AC C0B2 1F32
uid [ unknown] Ubuntu Archive Automatic Signing Key (2012) <[email protected]>
/etc/apt/trusted.gpg.d/ubuntu-keyring-2012-cdimage.gpg
------------------------------------------------------
pub rsa4096 2012-05-11 [SC]
8439 38DF 228D 22F7 B374 2BC0 D94A A3F0 EFE2 1092
uid [ unknown] Ubuntu CD Image Automatic Signing Key (2012) <[email protected]>
$ sudo apt-key del "BCCC C1E2 8354 33FA 7DB8 5D51 D45D F2E8 FC91 AE7E"
OK
$ sudo apt-key del "29D7 6ADA 2D15 A87B F4C6 8B82 3729 8274 54B8 C8AC"
OK
$ sudo apt-key del "1B32 B87A BAEE 3572 18F6 B48C B5B1 16B7 2D0F 61F0"
OK
$
Yeeeeee!
@mdooley
Good find, i learned something from that post 
I’m leaving this post open, since i cannot remove items from a list in the “Software & Updates”
That’s a bug that needs fixing.