Where can I find debug symbols for KDE Discover

I am trying to provide a backtrace for repeated crashes of KDE Discover, but cannot find (much less install) the needed debug files.
I have attempted to find debugging symbols for Discover by adding the following repositories to my Software Sources:

deb http://ddebs.ubuntu.com jammy main restricted universe multiverse
deb http://ddebs.ubuntu.com jammy-updates main restricted universe multiverse
deb http://ddebs.ubuntu.com jammy-security main restricted universe multiverse
deb http://ddebs.ubuntu.com jammy-proposed main restricted universe multiverse

as recommended in this thread:

How to install debug symbols for installed packages?

However, I was then prompted to refresh the cache, which produced the following error message:

Could not refresh cache
pk-client-error-quark: E: The repository 'http://ddebs.ubuntu.com jammy-security Release' does not have a Release file.
W: Updating from such a repository can't be done securely, and is therefore disabled by default.
W: See apt-secure(8) manpage for repository creation and user configuration details.
W: GPG error: http://ddebs.ubuntu.com jammy Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY C8CAB6595FDFF622
E: The repository 'http://ddebs.ubuntu.com jammy Release' is not signed.
W: Updating from such a repository can't be done securely, and is therefore disabled by default.
W: See apt-secure(8) manpage for repository creation and user configuration details.
W: GPG error: http://ddebs.ubuntu.com jammy-updates Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY C8CAB6595FDFF622
E: The repository 'http://ddebs.ubuntu.com jammy-updates Release' is not signed.
W: Updating from such a repository can't be done securely, and is therefore disabled by default.
W: See apt-secure(8) manpage for repository creation and user configuration details.
W: GPG error: http://ddebs.ubuntu.com jammy-proposed Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY C8CAB6595FDFF622
E: The repository 'http://ddebs.ubuntu.com jammy-proposed Release' is not signed.
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I have performed the recommended "sudo apt install ubuntu-dbgsym-keyring", but I am still unable to find or install Discover debug symbols to enable a backtrace of the problem.

I am posting this as an answer, even though it isn't one, because it is too long for a comment.

@George The first command above yielded:

Warning: apt-key is deprecated. Manage keyring files in trusted.gpg.d instead (see apt-key(8)).
Executing: /tmp/apt-key-gpghome.qiNcMjEc9W/gpg.1.sh --recv-keys --keyserver keyserver.ubuntu.com C8CAB6595FDFF622
gpg: key C8CAB6595FDFF622: "Ubuntu Debug Symbol Archive Automatic Signing Key (2016) <ubuntu-archive@lists.ubuntu.com>" 2 new signatures

Executing the 2nd command apparently updated all of the newly added repositories but one:

Err:13 http://ddebs.ubuntu.com jammy-security Release     
  404  Not Found [IP: 185.125.190.17 80]
Get:14 http://ddebs.ubuntu.com jammy-proposed Release [40.5 kB]
Reading package lists... Done                                         
E: The repository 'http://ddebs.ubuntu.com jammy-security Release' does not have a Release file.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.

However, I am still unable to find any "dbgsym" packages.

First, add the missing GPG key:
sudo apt-key adv --recv-keys --keyserver keyserver.ubuntu.com C8CAB6595FDFF622
sudo apt update
Try installing the symbols again.