Hi Alexander! 
Yeah I made an hour long Google search before I posted and I did not find any similar problem.
I tried the way you described above, but still… 
{"timestamp":"2023-01-30 08:29:39.152 +01:00","level":"info","msg":"Server is initializing...","caller":"platform/service.go:165","go_version":"go1.18.1"}
{"timestamp":"2023-01-30 08:29:39.152 +01:00","level":"info","msg":"Pinging SQL","caller":"sqlstore/store.go:238","database":"master"}
{"timestamp":"2023-01-30 08:29:39.153 +01:00","level":"error","msg":"Failed to ping DB","caller":"sqlstore/store.go:248","error":"pq: Could not detect default username. Please provide one explicitly","retrying in seconds":10}
{"timestamp":"2023-01-30 08:29:49.158 +01:00","level":"info","msg":"Pinging SQL","caller":"sqlstore/store.go:238","database":"master"}
{"timestamp":"2023-01-30 08:29:49.158 +01:00","level":"error","msg":"Failed to ping DB","caller":"sqlstore/store.go:248","error":"pq: Could not detect default username. Please provide one explicitly","retrying in seconds":10}
Anyway the versions are:
Docker version 20.10.12, build 20.10.12-0ubuntu2~20.04.1
docker-compose version 1.25.0, build unknown
(inside the compose the default 2.4)
Did I miss maybe any step regarding to postgres?
Thank you for your help!