Start the SDK--container interactively, mounting the current directory as /app in the container
$ docker run --rm -it -v $(pwd):/app mcr.microsoft.com/dotnet/sdk:5.0

Change to folder ./app which contains the ./src folder (/app/src)
# cd /app

Start the build using /app/src as source folder and writing to /app/out 
# dotnet publish -c Release -o out src

That's it, exit
# exit