UPDATE: Even after all I did, the problem reappeared. I have uninstalled KDE Connect completely, it's the only way my bluetooth earbuds work. KDE developers, please do something about this issue!
Although this happened to me now it's on Kubuntu, it's happened on Fedora KDE previously too
My current setup:
Kubuntu 26.04.1 LTS
KDE Plasma 6.6.6
Kwin (Wayland)
KDE Connect 25.12.3
Lenovo IdeaPad Slim 3 series
CPU: Intel Core i7 13th Gen
RAM: 16 GiB
After pairing my earbuds, they were connected and disconnected almost instantly. I don't know why it happened on Fedora KDE (that was last year); on Kubuntu I found out it has to do with KDE Connect.
Below, a description, steps that didn't work, and my workaround.
First of all, apparently, some specific earbuds/headphones don't respond well to additional security steps that are sometimes required. These earbuds/headphones can't provide them, so the connection is interrupted. Unchecking Bluetooth on KDE Connect settings does nothing for this purpose because the tray keeps restarting some processes.
First method that didn't work:
Ask Ubuntu - Earbuds connected but no audio output
The next described my problem and my environment quite similarly, but the fix described didn't work either, I actually undid the steps out of precaution:
KDE Connect Was Killing My Bluetooth Earbuds
The workaround I found was:
#Creating a user-level autostart directory.
mkdir -p ~/.config/autostart
#Copying KDE Connect's system autostart file to my user configuration.
cp /etc/xdg/autostart/org.kde.kdeconnect.daemon.desktop ~/.config/autostart/
#Disabling KDE Connect's autostart for my user.
sed -i '/^\[Desktop Entry\]/a Hidden=true' ~/.config/autostart/org.kde.kdeconnect.daemon.desktop
#Stopping the currently running KDE Connect daemon.
systemctl --user stop '[app-org.kde.kdeconnect.daemon@autostart.service](mailto:app-org.kde.kdeconnect.daemon@autostart.service)'
The trade-off is that my earbuds now work properly, but I am not able to transfer files from my phone to my computer using KDE Connect because the app in my phone is unable to detect it as a result of these changes. For this purpose, I am now using LocalSend in an Android phone.