ISO Level 3 Shift no longer works after upgrade from OpenSuSE Leap 15.5. to 15.6. Why?

After upgrading my OpenSuSE Leap system from version 15.5 to 15.6, the ISO Level 3 (aka AltGr) function map to the right Alt key suddenly no longer works. The key itself is recognised as such, though, as tested with xev (irrelavant output omitted):

╭─jacek@epica /usr/share/X11/xkb/symbols  
╰─➤  xev
KeyPress event, serial 40, synthetic NO, window 0x4300001,
    root 0x410, subw 0x0, time 7289615, (597,232), root:(1468,677),
    state 0x10, keycode 108 (keysym 0xfe03, ISO_Level3_Shift), same_screen YES,
    XKeysymToKeycode returns keycode: 92
    XLookupString gives 0 bytes: 
    XmbLookupString gives 0 bytes: 
    XFilterEvent returns: False

KeyRelease event, serial 40, synthetic NO, window 0x4300001,
    root 0x410, subw 0x0, time 7289735, (597,232), root:(1468,677),
    state 0x98, keycode 108 (keysym 0xfe03, ISO_Level3_Shift), same_screen YES,
    XKeysymToKeycode returns keycode: 92
    XLookupString gives 0 bytes: 
    XFilterEvent returns: False

Testing the keyboard layout with setxkbmap gives this result:

╭─jacek@epica /usr/share/X11/xkb/symbols  
╰─➤  setxkbmap -verbose 10
Setting verbose level to 10
locale is C
Trying to load rules file ./rules/evdev...
Trying to load rules file /usr/share/X11/xkb/rules/evdev...
Success.
Applied rules from evdev:
rules:      evdev
model:      pc105
layout:     de
variant:    pl
options:    compose:comp,terminate:ctrl_alt_bksp,lv3:ralt_switch,altwin:meta_win,grp:win_space_toggle
Trying to build keymap using the following components:
keycodes:   evdev+aliases(qwertz)
types:      complete
compat:     complete
symbols:    pc+de(pl)+inet(evdev)+altwin(meta_win)+terminate(ctrl_alt_bksp)+level3(ralt_switch)+group(win_space_toggle)
geometry:   pc(pc105)

level3(ralt_switch) should be the correct directive to turn the right Alt switch into ISO Level 3 Shift, or am I wrong? This is the system version:

╭─jacek@epica /usr/share/X11/xkb/symbols  
╰─➤  uname -a
Linux epica 6.4.0-150600.23.53-default #1 SMP PREEMPT_DYNAMIC Wed Jun  4 05:37:40 UTC 2025 (2d991ff) x86_64 x86_64 x86_64 GNU/Linux

The keyboard itself is a Sun Type 7 (German layout). So: Why does a system upgrade un-map AltGr? **UPDATE:** When defining an accelerator for a utility in the KDE system settings, I found out that typing +J resulted in Alt+ʒ. This is **not** the expected result, which would have been just the ʒ and nothing else. Maybe there is really a bug in the config. I ran xkbcomp :0 - to stumble over lines like these:

modifier_map Control {  };
    modifier_map Shift {  };
    modifier_map Shift {  };
    modifier_map Mod1 {  };
    modifier_map Lock {  };
    modifier_map Mod2 {  };
    modifier_map Mod5 {  };
    modifier_map Control {  };
    modifier_map Mod1 {  };
    modifier_map Mod4 {  };
    modifier_map Mod4 {  };
    modifier_map Mod3 {  };
    modifier_map Mod1 {  };
    modifier_map Mod4 {  };
    modifier_map Mod4 {  };
    modifier_map Mod4 {  };

Why is both `, and (= the key labeled AltGr) tied to Mod1? Isn't AltGr synonymous to Mod3`??