I am happy to report that I have fixed my issue. Here's the solution in case someone faces the same issue -

I added these two in dockerfile

# Set environment variable for the listening port, as required by Cloud Run
ENV ASPNETCORE_URLS=http://+:8080

ENV PORT 8080

FYI - I already had EXPOSE 8080 and yet, the above two lines were required. This makes sense, as the error suggested something about PORT 8080. However, I still do not understand why these two lines were required as it was working fine before. I wonder if it is because of the dotnet 9 upgrade. Let me know if anyone has a clue.

Cheers!