SUMMARY
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***


STEPS TO REPRODUCE
1. Set "English US" or "English UK" to first (top) keyboard layout
2. Install Viber (.deb or flatpak)
3. Try to start Viber

OBSERVED RESULT
1. Viber can't be started after being installed (neither .deb or flatpak version) under X11 when first keyboard layout is set to "English US" or "English UK"
2. Changing the keyboard layout set on top to other language (in my example to Bulgarian, because I'm from Bulgaria and I use both languages, so just changing places) fix the issue and Viber can start normally. Returning the first keyboard layout to English makes impossibe starting the app.
3. This issue is known for X11, but not for Wayland where the app starts normally.

EXPECTED RESULT
Opening Viber normally in X11 session no matter what language layout is set to be first.

SOFTWARE/OS VERSIONS
Windows: 
macOS: 
Linux/KDE Plasma: KDE Neon 5.26
(available in About System)
KDE Plasma Version: 5.26.2
KDE Frameworks Version: 5.99.0
Qt Version: 5.15.7

ADDITIONAL INFORMATION
Kernel Version: 5.15.0-52-generic (64-bit)
Graphics Platform: X11