I cannot launch Thunderbird successfully anymore after migrating to Ubuntu 20.10. There is an issue in syncing with Nextcloud Calendar but after dutifully marking this calendar as read-only from Thunderbird, I cannot get Thunderbird up anymore in subsequent sessions. Here is a snippet when I tried to launch Thunderbird from the command line:

reza@BeUlta:~$ thunderbird --offline [calBackendLoader] Using Thunderbird's libical backend Extension error: Error while loading 'jar:file:///usr/lib/thunderbird/extensions/messagingmenu@mozilla.com.xpi!/manifest.json' (NS_ERROR_FILE_NOT_FOUND) resource://gre/modules/Extension.jsm:570 :: readJSON/</<@resource://gre/modules/Extension.jsm:570:20 onStopRequest@resource://gre/modules/NetUtil.jsm:128:18 </p>

Extension error: Error while loading 'jar:file:///usr/lib/thunderbird/omni.ja!/chrome/messenger/search-extensions/twitter/manifest.json' (NS_ERROR_FILE_NOT_FOUND) resource://gre/modules/Extension.jsm:570 :: readJSON/</<@resource://gre/modules/Extension.jsm:570:20 onStopRequest@resource://gre/modules/NetUtil.jsm:128:18 </p>

Extension error: statusPrivacy is null resource://gdata-provider/legacy/modules/ui/gdata-event-dialog.jsm:56 :: gdataInitUI/<@resource://gdata-provider/legacy/modules/ui/gdata-event-dialog.jsm:56:5 gdataInitUI@resource://gdata-provider/legacy/modules/ui/gdata-event-dialog.jsm:60:5 onLoadWindow@resource://gdata-provider/legacy/modules/gdataUI.jsm:30:18 checkAndRunExtensionCode@resource:///modules/ExtensionSupport.jsm:220:28 _checkAndRunMatchingExtensions@resource:///modules/ExtensionSupport.jsm:192:31 registerWindowListener/<@resource:///modules/ExtensionSupport.jsm:71:26 registerWindowListener@resource:///modules/ExtensionSupport.jsm:70:22 registerWindowListener@resource://gdata-provider/legacy/modules/gdataUI.jsm:24:20 register@resource://gdata-provider/legacy/modules/gdataUI.jsm:49:25 onStartup@jar:file:///home/reza/.thunderbird/fe8oqzkl.default/extensions/%7Ba62ef8ec-5fdc-40c2-873c-223b8a6925cc%7D.xpi!/api/gdata.js:48:13 onStartup/<@resource://gre/modules/ExtensionCommon.jsm:1406:17

JavaScript error: chrome://enigmail/content/ui/enigmailMessengerOverlay.js, line 39: TypeError: document.getElementById(...) is null JavaScript error: chrome://enigmail/content/modules/subprocess.jsm, line 344: uncaught exception: Object JavaScript error: chrome://enigmail/content/modules/subprocess.jsm, line 344: uncaught exception: Object JavaScript error: , line 0: uncaught exception: Object JavaScript error: resource://gre/modules/ExtensionParent.jsm, line 1533: Error: Message manager was disconnected before receiving Extension:ExtensionViewLoaded reza@BeUlta:~$

When I click the Thunderbird icon in the Favorites navbar, I get two message boxes:

1. An error has occured. An error occured when writing to the calendar NextCloud! When this appeared for the first time, I read the details and marked the calendar as read only. Thunderbird would still launch and still complain with the same message. But now all of sudden, Thunderbird just quits after the message box is dismissed.

2. XML Parsing Error: undefined entity: XML Parsing Error: undefined entity Location: chrome://messenger/content/messenger.xhtml Line Number 905, Column 3:

 <key id="openLightningKey"
</pre>
--^
Please help! I'm dead in the water and I need to get Thunderbird up and running even with limited functionality as a workaround. Thanks for your help and advice.
Kind regards.