Please give more information about your installation.
Is it a new install or an update, which distribution, do you use package or docker-compose direct …
This can happen eg. if in an updated package installation the /usr/share/egroupware/phpgwapi
directory is left over (eg. because you copied some files there). In that case run the following commands:
mv /usr/share/egroupware/phpgwapi /tmp
cd /etc/egroupware-docker
docker-compose restart
Ralf