SUMMARY
I'm trying to customize the key shortcuts but I ran into an issue where a conflict is detected and supposedly solved when assigning the shortcut. When pressing the key combination, I get told to solve the ambiguity.

STEPS TO REPRODUCE
1. Go to Settings / Configure Keyboard Shortcuts.
2. Find "Move to Top of View" and assign "Ctrl+PgUp"
3. Get prompted with "The "Ctrl+PgUp" shortcut is ambiguous with the following shortcut. Do you want to assign an empty shortcut to this action? Shortcut 'Alt+Left' for action 'Previous Tab'"
4. Choose "Reassign".
5. Close the settings dialog and back in the edit window press "Ctrl+PgUp".

OBSERVED RESULT
A message pops up, stating: "The key sequence 'Ctrl+PgUp' is ambiguous. Use 'Configure Keyboard Shortcuts' from the 'Settings' menu to solve the ambiguity. No action will be triggered."

EXPECTED RESULT
The cursor should move to the top of the page.

SOFTWARE/OS VERSIONS
Linux/KDE Plasma: 
(available in About System)
KDE Plasma Version: Probably latest, as I'm on opeSUSE Tumbleweed. Not sure how to find it, but I don't see it in "About System"
KDE Frameworks Version: 5.106.0
Qt Version: 5.15.9

ADDITIONAL INFORMATION
Workaround:

Open "Configure Keyboard Shortcuts", find "Previous Tab" and unassign the alternate or make some other change (once I saw a Ctrl+PgUp there, but mostly it's "Back").
Open /home/$USER/.local/share/kxmlgui5/kate/kateui.rc go to the end, find view_prev_tab, and remove Ctrl+PgUp from its entry.

Before edit:
    <Action name="view_prev_tab" shortcut="Back; Ctrl+PgUp; Ctrl+["/>
After edit it's
    <Action name="view_prev_tab" shortcut="Back"/>