Yes, thank you very much.
I had to enable error logging first.
When trying to update, at first repeating a list of all plugins loaded.
DEBUG Piwik\Plugin\Manager[2023-02-01 11:33:16 UTC] [4f87b] Loaded plugins: CoreVue, CorePluginsAdmin, CoreAdminHome, CoreHome, WebsiteMeasurable, IntranetMeasurable, Diagnostics, CoreVisualizations, Proxy, API, Widgetize, Transitions, LanguagesManager, Actions, Dashboard, MultiSites, Referrers, UserLanguage, DevicesDetection, Goals, SEO, Events, UserCountry, GeoIp2, VisitsSummary, VisitFrequency, VisitTime, VisitorInterest, RssWidget, Feedback, Monolog, Login, TwoFactorAuth, UsersManager, SitesManager, Installation, CoreUpdater, CoreConsole, ScheduledReports, UserCountryMap, Live, PrivacyManager, ImageGraph, Annotations, MobileMessaging, Overlay, SegmentEditor, Insights, Morpheus, Contents, BulkTracking, Resolution, Heartbeat, Intl, Marketplace, ProfessionalServices, UserId, CustomJsTracker, Tour, PagePerformance, CustomDimensions
(repeated several times).
But then:
WARNING CoreUpdater[2023-02-01 11:35:36 UTC] [2d05c] /xxx/matomo/vendor/matomo/decompress/libs/PclZip/pclzip.lib.php(4183): Warning - unpack(): Type V: not enough input, need 4, have 0 - Matomo 4.13.1 - Please report this message in the Matomo forums: https://forum.matomo.org (please do a search first as it might have been reported already) [internal function]: Piwik\ErrorHandler::errorHandler(),#1/vendor/matomo/decompress/libs/PclZip/pclzip.lib.php(4183),#2/vendor/matomo/decompress/libs/PclZip/pclzip.lib.php(3224),#3/vendor/matomo/decompress/libs/PclZip/pclzip.lib.php(789),#4/vendor/matomo/decompress/src/PclZip.php(69),#5/plugins/CoreUpdater/Updater.php(243),#6/plugins/CoreUpdater/Updater.php(103),#7/plugins/CoreUpdater/Controller.php(178),[internal function]: Piwik\Plugins\CoreUpdater\Controller->oneClickUpdate(),#9/core/FrontController.php(631)
WARNING CoreUpdater[2023-02-01 11:35:36 UTC] [2d05c] /xxx/matomo/vendor/matomo/decompress/libs/PclZip/pclzip.lib.php(4186): Warning - Trying to access array offset on value of type bool - Matomo 4.13.1 - Please report this message in the Matomo forums: https://forum.matomo.org (please do a search first as it might have been reported already) #0/vendor/matomo/decompress/libs/PclZip/pclzip.lib.php(4186),#1/vendor/matomo/decompress/libs/PclZip/pclzip.lib.php(3224),#2/vendor/matomo/decompress/libs/PclZip/pclzip.lib.php(789),#3/vendor/matomo/decompress/src/PclZip.php(69),#4/plugins/CoreUpdater/Updater.php(243),#5/plugins/CoreUpdater/Updater.php(103),#6/plugins/CoreUpdater/Controller.php(178),[internal function]: Piwik\Plugins\CoreUpdater\Controller->oneClickUpdate(),#8/core/FrontController.php(631),#9/core/FrontController.php(169)
After this nothing more, wait a while, then comes 503.
What can I do now?