Since then Numlock is off on startup and thunderbird (the application set to autostart) does not autostart.
KDE5 system settings - input devices - keyboard has Numlock ‘switch on’ on Plasma start.
(Yast has that too under hardware - keyboardlayout -advanced.)
KDE5 system settings - start - autostart has thunderbird (switched on).
There have been several threads related to Numlock recently … have a look through the install and application sections, you should be able to find them (with plenty of info in regards to this provided therein such threads)