Upgrade process stops with an error #25598

Intended to upgrade with Web-Updater from
Nextcloud 19.0.8 -> Nextcloud 20.0.7
But stops with an error.

Update vorbereiten
Log-Level auf "debug" gesetzt
Wartungsmodus eingeschaltet
Reparaturschritt: Repair MySQL collation
Reparaturinformation: All tables already have the correct collation -> nothing to do
Reparaturschritt: Repair SQLite autoincrement
Reparaturschritt: Copy data from accounts table when migrating from ownCloud
Reparaturschritt: Drop account terms table when migrating from ownCloud
Das Datenbankschema wird aktualisiert
Doctrine\DBAL\Exception\DriverException: An exception occurred while executing 'ALTER TABLE oc_authtoken CHANGE password_invalid password_invalid TINYINT(1) DEFAULT '0'': SQLSTATE[42000]: Syntax error or access violation: 1071 Specified key was too long; max key length is 767 bytes

What happend before the Upgrade?

• Made Upgrades from 19.0.0 up to 19.08 without problems
• used 1 occ commands as told from nextcloud for mysql database optimization (bigint and so on)

sudo -u www-data php /var/www/nextcloud/occ db:convert-filecache-bigint

Operating system:
Raspberry Pi 3

Web server:
Apache

Database:
MySQL

PHP version:
PHP 7.3.25-1+020201130.73+debian91.gbp042074

What can I do now? Thanks in advance.