Make sure cookies are allowed in Thunderbird. See https://support.mozilla.org/kb/automatic-conversion-google-mail-accounts-oauth20

Thank you christ1. I carefully checked the conditions mentioned in the post. Cookies were already all allowed. The problem remains the same. I wonder whether the problem comes from the fact that I have several Google accounts. I have to choose one account before authorising.

Thank you christ1. I carefully checked the conditions mentioned in the post. Cookies were already all allowed. The problem remains the same. I wonder whether the problem comes from the fact that I have several Google accounts. I have to choose one account before authorising.

I wonder whether the problem comes from the fact that I have several Google accounts. I have to choose one account before authorising.

Multiple Gmail accounts shouldn't be a problem. Are you saying you do have a problem with one specific account only, and all others do work?

Please post your Troubleshooting Information. At the top right of the Thunderbird window, click the menu button ≡, then select Help > Troubleshooting Information. Press the "Copy text to clipboard button" and paste the information into your reply.

Hello. Always same problem with Google authentication, be it a new Google email account, a connection to Google contact, or a connection to a Google agenda. I can see the Google screen (in French) asking whether I accept sharing mails, contacts ang agenda with Thunderbird. After hiting "Accept", I come back to the TB configuration screen with "authentication failed". When trying to connect to Google Agenda, I have this sequence 4 times, that is the number of agendas I try to synchronize.

Hint: my "name" has accents (in French).

Here is the "Troubleshooting information" (without last section "Accélération graphique", because of space overflow).

 Paramètres de base de l’application

   Nom: Thunderbird
   Version: 150.0
   Identifiant de compilation: 20260416011526
   ID de distribution:

   Canal de mise à jour: release
   Agent utilisateur: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:150.0) Gecko/20100101 Thunderbird/150.0
   Système d’exploitation: Windows_NT 10.0 26200
   Thème du système d’exploitation:

   Processus de lancement: Activé
   Fenêtres multiprocessus: 0/0
   Fenêtres Fission: 0/0
             Activées par défaut
   Processus distants: 7
   Stratégies d’entreprise: Inactives
   Clé du service de localisation de Google: Manquante
   Clé de Google Safebrowsing: Manquante
   Clé du service de localisation de Mozilla: Manquante
   Mode sans échec: false
   Taille de la mémoire (RAM): 7,7 Go
   Espace disque disponible: 170 Go

 Comptes courrier et groupes
   account1:
     INCOMING: account1, , (imap) imap.orange.fr:993, SSL, passwordCleartext
     OUTGOING: , smtp.orange.fr:465, SSL, passwordCleartext, true

   account2:
     INCOMING: account2, , (none) Local Folders, plain, passwordCleartext

   account3:
     INCOMING: account3, , (imap) ssl0.ovh.net:993, SSL, passwordCleartext
     OUTGOING: , ssl0.ovh.net:465, SSL, passwordCleartext, true

   account5:
     INCOMING: account5, , (imap) imap.orange.fr:993, SSL, passwordCleartext
     OUTGOING: , smtp.orange.fr:465, SSL, passwordCleartext, true

   account6:
     INCOMING: account6, , (imap) ssl0.ovh.net:993, SSL, passwordCleartext
     OUTGOING: , ssl0.ovh.net:465, SSL, passwordCleartext, true

   account8:
     INCOMING: account8, , (imap) ssl0.ovh.net:993, SSL, passwordCleartext
     OUTGOING: , ssl0.ovh.net:465, SSL, passwordCleartext, true

   account9:
     INCOMING: account9, , (imap) ssl0.ovh.net:993, SSL, passwordCleartext
     OUTGOING: , ssl0.ovh.net:465, SSL, passwordCleartext, true

   account10:
     INCOMING: account10, , (imap) ssl0.ovh.net:993, SSL, passwordCleartext
     OUTGOING: , ssl0.ovh.net:465, SSL, passwordCleartext, true

   account11:
     INCOMING: account11, , (imap) ssl0.ovh.net:993, SSL, passwordCleartext
     OUTGOING: , ssl0.ovh.net:465, SSL, passwordCleartext, true

   account12:
     INCOMING: account12, , (imap) ssl0.ovh.net:993, SSL, passwordCleartext
     OUTGOING: , ssl0.ovh.net:465, SSL, passwordCleartext, true

 Bibliothèques

     Bibliothèque
     État
     Version minimale attendue
     Version utilisée
     Chemin

       RNP (OpenPGP)
       OK
       0.18.1
       0.18.1.MZLA.150.0.botan.3.8.1
       C:\Program Files\Mozilla Thunderbird\rnp.dll

       OTR
       Échec du chargement. Le chiffrement des discussions OTR ne fonctionnera pas.
       -
       -
       -

 Paramètres de l’agenda

   Mon agenda

     Nom
     Valeur

     Nom:
     Type: storage
     Désactivé: false
     Nom d’utilisateur:
     URI:
     Intervalle d’actualisation:
     En lecture seule:
     Supprimer les alarmes:
     Cache activé:
     Identité iMIP: id2
     iMIP désactivé:
     Compte iMIP:
     Identifiant de l’organisateur:
     Forcer la planification des messages:
     Alarmes contextuelles prises en charge:
     Alarmes sur invitation prises en charge:
     Alarmes maximales par évènement:
     Pièce jointe prise en charge:
     Catégories maximales:
     État de confidentialité pris en charge:
     Priorité prise en charge: true
     Évènement pris en charge:
     Tâche prise en charge:
     Heure locale prise en charge:
     UTC/GMT pris en charge:
     Programmation automatique prise en charge:

 Rapports de plantage des 3 derniers jours

 Processus distants

   Type: Nombre

     Pages « à propos » privilégiées: 1
     RDD: 1
     Contenu web isolé: 1
     Extension: 1
     GPU: 1
     Utilitaire Windows Media Foundation: 1
     Utilitaire Décodeur audio générique: 1

 Modules complémentaires

     Nom
     Type
     Version
     Activé
     Emplacement
     ID

       FileLink Provider for Dropbox
       extension
       7
       true
       app-profile
       dropbox-cloudfile@darktrojan.net

       Signal Spam
       extension
       4.2.9
       true
       app-profile
       signal-spam@signal-spam.fr

       Thème système — automatique
       theme
       1.4.2
       true
       app-builtin
       default-theme@mozilla.org

       Clair
       theme
       1.3.2
       false
       app-builtin
       thunderbird-compact-light@mozilla.org

       Sombre
       theme
       1.3.2
       false
       app-builtin
       thunderbird-compact-dark@mozilla.org

 Logiciel de sécurité

   Type: Nom

     Antivirus: Antivirus Microsoft Defender
     Logiciel anti-espion:
     Pare-feu: Pare-feu Windows

 Anciennes feuilles de style utilisateur

   Activées: false
   Feuilles de style: Aucune feuille de style trouvée

Beyond cookies, make sure not to use a VPN while authenticating. Also make sure there is no other process running on your computer listening on TCP port 80, e.g. like a local web server. To test whether something is listing on port 80, in a command/dos window: netstat -an | findstr LISTEN | findstr ":80[^0-9]"