Here is a list of what was fixed since 11.5.8:

• 2022-04-12 41418975d3 [RELEASE] Release of TYPO3 11.5.9 (thanks to Oliver Hader)
• 2022-04-11 f8088b416c [BUGFIX] Prevent JavaScript error on changing single option group fields (thanks to Oliver Bartsch)
• 2022-04-11 bc4093afba [DOCS] Align with new TYPO3 documentation standards (thanks to Alexander Nitsche)
• 2022-04-08 8005da651f [BUGFIX] Correct the description for the cache:warmup command (thanks to Shehfinaz Kadavil)
• 2022-04-08 b59f0153ae [TASK] Apply dark style to module menu scrollbar (thanks to Benjamin Franzke)
• 2022-04-08 92a9671c4c [BUGFIX] Avoid race conditions in pagetree contextmenu actions (thanks to Benjamin Franzke)
• 2022-04-08 1758dd3685 [BUGFIX] Check for undefined fileTarget (thanks to Georg Ringer)
• 2022-04-08 224f8511ba [TASK] Remove superfluous eval declarations (thanks to Oliver Bartsch)
• 2022-04-07 8a6cedc250 [BUGFIX] Prevent duplicate contextmenu in page tree nodes (thanks to Benjamin Franzke)
• 2022-04-07 0ec79fa513 [BUGFIX] Remove unnecessary row/col from clipboard (thanks to Andreas Fernandez)
• 2022-04-07 14fbe96560 [BUGFIX] Fix duration determination in Notification.showMessage() (thanks to Andreas Fernandez)
• 2022-04-07 343bfadbe8 [BUGFIX] Fix exception in filelist when nullable columns are shown (thanks to Torben Hansen)
• 2022-04-06 7b12ba8441 [BUGFIX] Align functional splitting to chunk execution (thanks to Stefan Bürk)
• 2022-04-05 fbb6f47894 [TASK] Use ckeditor's native readOnly mode (thanks to Andreas Fernandez)
• 2022-04-05 b59ecd3a7d [BUGFIX] Explicitly use control characters in HTML fixture (thanks to Andreas Fernandez)
• 2022-04-05 34d3457613 [TASK] Apply new documentation standard definitions (thanks to Simon Gilli)
• 2022-04-05 8ecc7bee41 [BUGFIX] Show correct creation and modification time in filelist (thanks to Oliver Bartsch)
• 2022-04-04 d045043caa [TASK] Comment two symfony/rate-limiter related tests (thanks to Christian Kuhn)
• 2022-04-04 726fadae9a [BUGFIX] Allow filelist sorting by creation date (thanks to Georg Ringer)
• 2022-04-01 9763ce5287 [BUGFIX] Prevent invalid array access warnings in DataHandler (thanks to Oliver Bartsch)
• 2022-04-01 b2f4f54531 [BUGFIX] Add guard clause to prevent fataling on saving a CE (thanks to Jan Helke)
• 2022-04-01 eeb5af4f27 [BUGFIX] Accept native TIME value '00:00:00' in backend forms (thanks to Oliver Hader)
• 2022-03-31 13f67e3610 [TASK] runTests.sh: Remove .csv integrity handling (thanks to Christian Kuhn)
• 2022-03-31 be12204485 [BUGFIX] Add guard clause to prevent Link Browser from fataling (thanks to Jan Helke)
• 2022-03-29 3693c1cc27 [BUGFIX] Load property from real instance (thanks to Simon Schaufelberger)
• 2022-03-29 c6c053ca3f [BUGFIX] Apply proper styles to checkbox in mass undo modal (thanks to Oliver Bartsch)
• 2022-03-29 3b44d06101 [BUGFIX] Ensure imageLinkWrap works with UTF-8 filenames (thanks to Lars Michalowski)
• 2022-03-29 16f3c51cf2 [BUGFIX] Remove usage of undefined variable (thanks to Georg Ringer)
• 2022-03-29 925e71a275 [DOCS] Fixed spelling of "includeJSFooterlibs" (thanks to Eric Bode)
• 2022-03-29 8f3f782a43 [BUGFIX] Remove double encoding and improve template (thanks to Simon Schaufelberger)
• 2022-03-28 b97ab48ae8 [BUGFIX] Respect delimiter/enclosure in table ctype (thanks to Jochen Roth)
• 2022-03-28 ba367bf0d1 [BUGFIX] Avoid PHP 8.1 warning passing null format to DateViewHelper (thanks to Chris Müller)
• 2022-03-28 2afcdf6ab1 [BUGFIX] Bring back functionality for $uniqueIds in SelectSingleElement (thanks to Nikita Hovratov)
• 2022-03-28 e12f4d8dce [TASK] Inform about not found user in record history (thanks to Oliver Bartsch)
• 2022-03-28 6a349ce9d3 [BUGFIX] Avoid PHP 8.x error in RecordHistory if BE user is missing (thanks to Jan Helke)
• 2022-03-26 84674dfee1 [BUGFIX] Upgrade to CKEditor4 v4.18.0 (thanks to Oliver Hader)
• 2022-03-25 5e5a87d426 [BUGFIX] Upgrade guzzlehttp/psr7 to latest version (thanks to Oliver Hader)
• 2022-03-25 a156c879b7 [BUGFIX] Properly add crop variants parameter to preview url (thanks to Oliver Bartsch)
• 2022-03-24 d4fd332544 [BUGFIX] Fix undefined array key warning in GifBuilder (thanks to Simon Schaufelberger)
• 2022-03-23 731e52f93f [BUGFIX] Execute symfony commands in scheduler as non-interactive (thanks to Oliver Bartsch)
• 2022-03-23 ac01166a86 [BUGFIX] Fix notice in SearchController (thanks to Georg Ringer)
• 2022-03-23 d947c50beb [TASK] Raise friendsofphp/php-cs-fixer:^3.8.0 (thanks to Oliver Bartsch)
• 2022-03-22 8f45e1180d [BUGFIX] Trigger change event in typo3-backend-table-wizard (thanks to Oliver Hader)
• 2022-03-22 e9a6623740 [BUGFIX] Raise doctrine/dbal:^2.13.8 (thanks to Stefan Bürk)
• 2022-03-21 ad1c7f8bca [BUGFIX] Prevent undefined array key warning in FormPersistenceManager (thanks to Oliver Bartsch)
• 2022-03-21 94c3948ed5 [BUGFIX] Prevent TypeError for unsupported operand types (thanks to Oliver Bartsch)
• 2022-03-21 89999f8e9b [TASK] Remove doc comments for TYPO3\CMS\Core\Cache\Frontend\FrontendInterface (thanks to Simon Schaufelberger)
• 2022-03-21 972755d9c6 [BUGFIX] Consider all relevant pids when populating BE TS constants (thanks to Susanne Moog)
• 2022-03-21 1e27f6d430 [TASK] Update HTML Sanitizer (thanks to Benni Mack)
• 2022-03-18 ed0fe37ba8 [BUGFIX] Handle missing BE_USER in ext manager (thanks to Markus Klein)
• 2022-03-17 04bc55a753 [BUGFIX] Prevent undefined array key in TemplateAnalyzerController (thanks to dev-rke)
• 2022-03-17 9efafbb092 [BUGFIX] Fix PHP deprecation on retrieving file / folder object (thanks to dev-rke)
• 2022-03-15 02652b6986 [BUGFIX] Use INSERT Action when copying records in DataHandler (thanks to Benni Mack)
• 2022-03-15 515973dd52 [BUGFIX] Add record title of content in InternalLinkType (thanks to Oliver Bartsch)
• 2022-03-14 fde62fd264 [BUGFIX] Use sys_history for workspaces stage changes + comments (thanks to Benni Mack)
• 2022-03-14 b1cb4f2789 [BUGFIX] Avoid undefined array key warnings in PreviewUriBuilder (thanks to Francois Suter)
• 2022-03-11 6c0a4c45d2 [BUGFIX] Avoid undefined array key warning in deleteL10nOverlayRecords (thanks to Nikita Hovratov)
• 2022-03-10 50393e8918 [BUGFIX] Avoid notice in SuggestWizardController (thanks to Georg Ringer)
• 2022-03-10 41fb5cf395 [DOCS] Fix code example in EXT:redirects documentation (thanks to criwe)
• 2022-03-10 c56b9d7622 [TASK] Update to PHPStan 1.4.9 (thanks to Oliver Bartsch)
• 2022-03-10 fab7e73f9f [DOCS] Add missing ' in code example (thanks to criwe)
• 2022-03-09 c34067c45d [BUGFIX] Remove variables directly from log messages "details" field (thanks to Benni Mack)
• 2022-03-09 7437023fb9 [BUGFIX] Unify handling of reading from sys_log.log_data (thanks to Benni Mack)
• 2022-03-09 10748c5884 [BUGFIX] Check array key uid before accessing it (thanks to Georg Ringer)
• 2022-03-08 08ba1311cc [TASK] Set TYPO3 version to 11.5.9-dev (thanks to Benni Mack)