Since for software/OS update, PPA can play a vital role. So:
- Should I enable them all? Or should I enable those which say "Disco"?
- Or should I remove all which doesn't say "Disco"?
App update is important. Running "apt-get update" doesn't check for update unless I resolve this issue.
Just in case, this might be useful for this case:
$ ls /etc/apt/sources.list.d/
alexlarsson-ubuntu-flatpak-cosmic.list
alexlarsson-ubuntu-flatpak-cosmic.list.save
apandada1-ubuntu-brightness-controller-cosmic.list
apandada1-ubuntu-brightness-controller-cosmic.list.save
bit-team-ubuntu-stable-cosmic.list
bit-team-ubuntu-stable-cosmic.list.distUpgrade
bit-team-ubuntu-stable-cosmic.list.save
communitheme-ubuntu-ppa-cosmic.list
communitheme-ubuntu-ppa-cosmic.list.save
gnome-shell-extensions-ubuntu-ppa-cosmic.list
gnome-shell-extensions-ubuntu-ppa-cosmic.list.distUpgrade
gnome-shell-extensions-ubuntu-ppa-cosmic.list.save
google-chrome.list
google-chrome.list.distUpgrade
google-chrome.list.save
libreoffice-ubuntu-ppa-cosmic.list
libreoffice-ubuntu-ppa-cosmic.list.distUpgrade
libreoffice-ubuntu-ppa-cosmic.list.save
mysql.list
mysql.list.distUpgrade
mysql.list.save
ne0sight-ubuntu-chrome-gnome-shell-cosmic.list
ne0sight-ubuntu-chrome-gnome-shell-cosmic.list.save
noobslab-ubuntu-apps-cosmic.list
noobslab-ubuntu-apps-cosmic.list.distUpgrade
noobslab-ubuntu-apps-cosmic.list.save
noobslab-ubuntu-icons-cosmic.list
noobslab-ubuntu-icons-cosmic.list.distUpgrade
noobslab-ubuntu-icons-cosmic.list.save
noobslab-ubuntu-themes-cosmic.list
noobslab-ubuntu-themes-cosmic.list.distUpgrade
noobslab-ubuntu-themes-cosmic.list.save
oguzhaninan-ubuntu-stacer-cosmic.list
oguzhaninan-ubuntu-stacer-cosmic.list.save
rvm-ubuntu-smplayer-cosmic.list
rvm-ubuntu-smplayer-cosmic.list.save
scribus-ubuntu-ppa-cosmic.list
scribus-ubuntu-ppa-cosmic.list.distUpgrade
scribus-ubuntu-ppa-cosmic.list.save
shutter-ubuntu-ppa-cosmic.list
shutter-ubuntu-ppa-cosmic.list.save
sublime-text.list
sublime-text.list.distUpgrade
sublime-text.list.save
ubuntu-mozilla-security-ubuntu-ppa-cosmic.list
ubuntu-mozilla-security-ubuntu-ppa-cosmic.list.save
umang-ubuntu-indicator-stickynotes-cosmic.list
umang-ubuntu-indicator-stickynotes-cosmic.list.distUpgrade
umang-ubuntu-indicator-stickynotes-cosmic.list.save
vscode.list
vscode.list.distUpgrade
vscode.list.save
webupd8team-ubuntu-java-cosmic.list
webupd8team-ubuntu-java-cosmic.list.distUpgrade
webupd8team-ubuntu-java-cosmic.list.save
windscribe-repo.list
windscribe-repo.list.distUpgrade
windscribe-repo.list.save
Personal Package Archives (PPA) are used to install packages which are not in official repositories of Ubuntu or they contain an old version of the package. So, using a PPA solely depends on the needs of a user, like which packages he need.
Since Disco released a while ago, so all PPAs are not ready. You need to verify by going to PPA's page and check if they have ported packages for Disco as well (looks like a tedious task). If you use other distributions' PPA, it might create inconsistency, dependency problems or even break your system.
In the screenshot you attached in the question, most PPAs are for Source Code. If want Source Code, you can enable them. I'll say it is safe to enable repositories you need that mentions "Disco".
PPA basically contains three parts: URI, distribution and component. In most of the cases URI and components remain same but distribution changes. If you want to modify all 3rd party PPAs in one go for Disco, run:
After that you can enable all repositories (if you need them). If you get some errors like "Release file not found", it means PPA isn't ready for Disco yet. So, it's better to let it be disabled.
Additional Info: It seems you are using webupd8team's PPA for Oracle's JDK. But this PPA has been discontinued as of April 16, 2019 (reference). So it's better to delete it.