MailCow Update by script returned the following hint:

First of all, it is necessary to upgrade Docker Compose version v2:

https://docs.docker.com/compose/install/compose-plugin/#installing-compose-on-linux-systems

Subsequently, the following error message appears during the update attempt:

* error decoding 'Ports': Invalid ip address :: address ::: too many colons in address
Oh no, something went wrong. Please check the error message above.

Bug is fixed with a change in docker-compose.yml in line 379 to 381:

ports: 
- "${HTTPS_BIND:-0.0.0.0}:${HTTPS_PORT:-443}:${HTTPS_PORT:-443}" 
- "${HTTP_BIND:-0.0.0.0}:${HTTP_PORT:-80}:${HTTP_PORT:-80}"

(Source: https://github.com/mailcow/mailcow-dockerized/issues/4618#issuecomment-1148755429)

Afterwards, the update runs through flawlessly via the update.sh script: