Thanks for all the links, unfortunately none of the proposed solutions worked. Strange but I don’t know why.
What actually worked was a small change in traefik.service. I mount a folder with my CA certs with
–volume=./ca-certificates:/usr/local/share/ca-certificates:z
and added a second ExecStartPost line:
ExecStartPost=-runagent write-hosts
ExecStartPost=-podman exec -ti traefik update-ca-certificates
I didn’t expect this syntax, to be honest.