Docker manifest mismatch arm/v7 within aarch64 system

I am super new to Raspberry Pi’s and just tried to set up the server via Docker on my R Pi 4 with 8 GB Ram.
The version itruns on is aarch64, yet when I run “sudo docker-compose pull” it succesfully pulls rocketchat but not mongo:
ERROR: no matching manifest for linux/arm/v7 in the manifest list entries

My suspision is, that my docker-compose.yml is incorrect:
version: “3”
image: rocketchat/
- ROOT_URL=http://999.999.9.999:3000
// the 9’s are used instead of my true IP
- 3000:3000
image: mongo:4.2

The Pi should be up to date and has Node.js and npm fully installed too.
I have read about “WiredTiger” engine being required but have no idea how to utilise that.

Thanks in advance for the help, best regards