[gbm]

Close calibre then open a terminal and enter:

sudo apt install xcb-cursor0

Now open calibre in debug mode using:

calibre-debug --gui

in the terminal open the Viewer then paste the debug log from the terminal.

bernie

edit:
your debug should look close to this:

Spoiler:

$ calibre-debug --gui
calibre 9.4  embedded-python: True
Linux-6.17.0-14-generic-x86_64-with-glibc2.39 Linux ('64bit', 'ELF')
('Linux', '6.17.0-14-generic', '#14~24.04.1-Ubuntu SMP PREEMPT_DYNAMIC Thu Jan 15 15:52:10 UTC 2')
Python 3.14.2
Interface language: None
EXE path: /opt/calibre/bin/calibre-debug
Successfully initialized third party plugins: ACSM Input (0, 1, 0) && Gather KFX-ZIP (from KFX Input) (2, 29, 0) && DeDRM (10, 0, 9) && Package KFX (from KFX Input) (2, 29, 0) && ACSM Input Plugin GUI Extension (0, 1, 0) && Baen (1, 2, 0) && Diaps Editing Toolbag (0, 5, 0) && EpubMerge (3, 2, 0) && EpubSplit (3, 12, 0) && KFX metadata reader (from KFX Input) (2, 29, 0) && From KFX (2, 29, 0) && KFX Input (2, 29, 0) && KindleUnpack - The Plugin (0, 83, 8) && Kobo Utilities (2, 27, 1) && Modify ePub (1, 8, 9)
QPA platform: xcb
devicePixelRatio: 1.09375
logicalDpi: 96.0 x 96.0
physicalDpi: 84.74714828897338 x 84.69527027027027
ApplicationPaletteChange event ignored
Using calibre Qt style: True
[0.00] Starting up...
System Color Scheme changed to: ColorScheme.Light
[0.00] Showing splash screen...
[1.24] splash screen shown
[1.25] Initializing db...
[1.87] db initialized
[1.87] Constructing main UI...
[2.99] [DEBUG] [koboutilities.config:<module>:73] CreateNewCustomColumn is supported
ACSM Input: GUI Plugin Genesis!
[3.54] [DEBUG] [koboutilities.action:KoboUtilitiesAction.genesis:120] Running in optimized mode
[4.24] GUI main window shown
EpubMerge: DEBUG: 2026-03-07 10:39:40,277: calibre_plugins.epubmerge.epubmerge_plugin(156): macmenuhack file_path:/home/username/.config/calibre/plugins/fanficfare_macmenuhack.txt
[4.28] [DEBUG] [koboutilities.config:get_library_config:646] library_config: {
    "SchemaVersion": 1,
    "profiles": {
        "Default": {
            "customColumnOptions": {
                "currentReadingLocationColumn": "",
                "lastReadColumn": "",
                "percentReadColumn": "",
                "ratingColumn": "rating",
                "restOfBookEstimateColumn": "",
                "timeSpentReadingColumn": ""
            },
            "forDevice": "*Any Device",
            "profileName": "Default",
            "storeOptionsStore": {
                "doNotStoreIfReopened": false,
                "promptToStore": true,
                "storeIfMoreRecent": false,
                "storeOnConnect": false
            },
            "updateOptionsStore": {
                "doEarlyFirmwareUpdate": false,
                "doFirmwareUpdateCheck": false,
                "firmwareUpdateCheckLastTime": 0
            }
        }
    },
    "readingPositionChangesStore": {
        "selectBooksInLibrary": false,
        "updeateGoodreadsProgress": false
    },
    "shelvesColumn": null
}
[4.28] [DEBUG] [koboutilities.action:KoboUtilitiesAction.set_toolbar_button_tooltip:180] setting to text='Utilities to use with Kobo ereaders

Driver: KoboTouch'
[4.41] main UI initialized...
[4.41] Hiding splash screen
[4.42] splash screen hidden
[4.42] Started up in 4.42 seconds with 3967 books
Worker Launch took: 0.00 seconds
GLX: Disable GBM because Ozone X11 is not available. Possibly caused by missing libraries for qpa-xcb support.
GBM is not supported with the current configuration. Fallback to Vulkan rendering in Chromium.

Originally Posted by paperback

Linux Mint 21 / Cinnamon 5.4.12

The Editor/Viewer crashes repeatedly on opening. Eventually after several attempts it does run successfully, and as expected.

This problem started some time back in version 3 and has continued through veriosn 4.