{Note: had a stroke in 2011 and am brain-damaged with really bad short term memory loss}

Aptitude, and other ways of downloading package stopped working.

I did a TEMPORARY fix, though.

The culprit was Opera-stable having too many different GPG keys. I temporarily "hash-tagged" out of existence via '#', and it works fine, but I can no longer get an update for Opera-stable.

I cannot figure how, exactly, can I remove the excess GPG keys?

Thank you for reading my question, and have an excellent day!

What about uncommenting one key at a time and seeing which one lets you update. Then you can get rid of the others.

I looked at all the opera-stable keys, I deleted everyone other than the current on {still active until about 1_1/2 years from now}.
I then removed the '#' symbol at the opera-stable one and it doesn't work again.

It now says, three times in a row:
"E: Conflicting values for option Signed-By regarding source https://deb.opera.com/opera-stable/ stable: /usr/share/keyrings/opera-browser.gpg !="

{And, yes, that key is a binary file}

And once at the end:
"E: The list of sources could not be read."

The entry in question in /etc/apt/sources-list.d:
deb https://deb.opera.com/opera-stable/ stable non-free %Opera Browser (final releases)

Sooo... it seems to be screwed up, although I have done this several times when "netinstalling" within the past month, with success, I don't know what happened this time.

I guess I could purge the opera-stable package, kill all the opera-stable keys, and go get the package again.....

{{I generally use Brave Browser, but for some things, Opera Browser has a built-in VPN, and it is easy to turn it on.....}}

Final update:

Although I put the "octothorpe"/"hash mark" {check it, the '#' symbol is called the "octothorpe"} to deal with the something-or-other, Opera-stable still updates.

Go figure!