@EJL, I had already tried that.
@pierre_a , thanks for the pointers. The log in the Mautic admin gives me only this error and only after I tried to access a contact again:
[2022-05-20 21:14:21] mautic.ERROR: Doctrine\DBAL\Exception\InvalidFieldNameException: An exception occurred while executing ‘SELECT t0.id AS id_1, t0.tag AS tag_2, t0.description AS description_3 FROM mtc_lead_tags t0 INNER JOIN mtc_lead_tags_xref ON t0.id = mtc_lead_tags_xref.tag_id WHERE mtc_lead_tags_xref.lead_id = ? ORDER BY t0.tag ASC’ with params [“3110”]: SQLSTATE[42S22]: Column not found: 1054 Unknown column ‘t0.description’ in ‘field list’ - in file /home/myusername/public_html/mautic/vendor/doctrine/dbal/lib/Doctrine/DBAL/Driver/AbstractMySQLDriver.php - at line 79