I had a 21.04 system that gave no warnings when I ran apt update, but then I ran this command (suggested by the internet)
add-apt-repository universe
and after that I get warnings when running
apt update
The warnings are
W: Skipping acquire of configured file 'universe/binary-amd64/Packages' as repository 'http://archive.canonical.com/ubuntu hirsute InRelease' doesn't have the component 'universe' (component misspelt in sources.list?)
W: Skipping acquire of configured file 'universe/binary-i386/Packages' as repository 'http://archive.canonical.com/ubuntu hirsute InRelease' doesn't have the component 'universe' (component misspelt in sources.list?)
W: Skipping acquire of configured file 'universe/i18n/Translation-sv' as repository 'http://archive.canonical.com/ubuntu hirsute InRelease' doesn't have the component 'universe' (component misspelt in sources.list?)
W: Skipping acquire of configured file 'universe/i18n/Translation-sv_SE' as repository 'http://archive.canonical.com/ubuntu hirsute InRelease' doesn't have the component 'universe' (component misspelt in sources.list?)
W: Skipping acquire of configured file 'universe/i18n/Translation-en' as repository 'http://archive.canonical.com/ubuntu hirsute InRelease' doesn't have the component 'universe' (component misspelt in sources.list?)
W: Skipping acquire of configured file 'universe/dep11/Components-amd64.yml' as repository 'http://archive.canonical.com/ubuntu hirsute InRelease' doesn't have the component 'universe' (component misspelt in sources.list?)
W: Skipping acquire of configured file 'universe/dep11/icons-48x48.tar' as repository 'http://archive.canonical.com/ubuntu hirsute InRelease' doesn't have the component 'universe' (component misspelt in sources.list?)
W: Skipping acquire of configured file 'universe/dep11/icons-64x64.tar' as repository 'http://archive.canonical.com/ubuntu hirsute InRelease' doesn't have the component 'universe' (component misspelt in sources.list?)
W: Skipping acquire of configured file 'universe/dep11/icons-64x64@2.tar' as repository 'http://archive.canonical.com/ubuntu hirsute InRelease' doesn't have the component 'universe' (component misspelt in sources.list?)
W: Skipping acquire of configured file 'universe/cnf/Commands-amd64' as repository 'http://archive.canonical.com/ubuntu hirsute InRelease' doesn't have the component 'universe' (component misspelt in sources.list?)
Here is the content of my /etc/apt/sources.list
# deb cdrom:[Ubuntu 20.04 LTS _Focal Fossa_ - Release amd64 (20200423)]/ focal main restricted
See http://help.ubuntu.com/community/UpgradeNotes for how to upgrade to
newer versions of the distribution.
deb http://se.archive.ubuntu.com/ubuntu/ hirsute main restricted
deb-src http://se.archive.ubuntu.com/ubuntu/ focal main restricted
Major bug fix updates produced after the final release of the
distribution.
deb http://se.archive.ubuntu.com/ubuntu/ hirsute-updates main restricted
deb-src http://se.archive.ubuntu.com/ubuntu/ focal-updates main restricted
N.B. software from this repository is ENTIRELY UNSUPPORTED by the Ubuntu
team. Also, please note that software in universe WILL NOT receive any
review or updates from the Ubuntu security team.
deb http://se.archive.ubuntu.com/ubuntu/ hirsute universe
deb-src http://se.archive.ubuntu.com/ubuntu/ focal universe
deb http://se.archive.ubuntu.com/ubuntu/ hirsute-updates universe
deb-src http://se.archive.ubuntu.com/ubuntu/ focal-updates universe
N.B. software from this repository is ENTIRELY UNSUPPORTED by the Ubuntu
team, and may not be under a free licence. Please satisfy yourself as to
your rights to use the software. Also, please note that software in
multiverse WILL NOT receive any review or updates from the Ubuntu
security team.
deb http://se.archive.ubuntu.com/ubuntu/ hirsute multiverse
deb-src http://se.archive.ubuntu.com/ubuntu/ focal multiverse
deb http://se.archive.ubuntu.com/ubuntu/ hirsute-updates multiverse
deb-src http://se.archive.ubuntu.com/ubuntu/ focal-updates multiverse
N.B. software from this repository may not have been tested as
extensively as that contained in the main release, although it includes
newer versions of some applications which may provide useful features.
Also, please note that software in backports WILL NOT receive any review
or updates from the Ubuntu security team.
deb http://se.archive.ubuntu.com/ubuntu/ hirsute-backports main restricted universe multiverse
deb-src http://se.archive.ubuntu.com/ubuntu/ focal-backports main restricted universe multiverse
Uncomment the following two lines to add software from Canonical's
'partner' repository.
This software is not part of Ubuntu, but is offered by Canonical and the
respective vendors as a service to Ubuntu users.
deb http://archive.canonical.com/ubuntu hirsute partner universe
deb-src http://archive.canonical.com/ubuntu focal partner
deb http://security.ubuntu.com/ubuntu hirsute-security main restricted
deb-src http://security.ubuntu.com/ubuntu focal-security main restricted
deb http://security.ubuntu.com/ubuntu hirsute-security universe
deb-src http://security.ubuntu.com/ubuntu focal-security universe
deb http://security.ubuntu.com/ubuntu hirsute-security multiverse
deb-src http://security.ubuntu.com/ubuntu focal-security multiverse
This system was installed using small removable media
(e.g. netinst, live or single CD). The matching "deb cdrom"
entries were disabled at the end of the installation process.
For information about how to configure apt package sources,
see the sources.list(5) manual.
EDIT: Added /etc/apt/sources.list and tried to clarify what I did to mess up my system.
cat /etc/apt/sources.list. In your edit you should also provide more context about your activities since the last time you successfully performed updates. In particular, share the details of alterations you made to your sources. – Nmath Jul 19 '21 at 20:35