create cron job using function on app platform or standard alone function

I want to create a cronjob to do some operations in database. I tried both function on app platform and standard alone function. However, there are issues with both ways:

1. function on app platform: cannot add “trigger” in project.yml file.
2. standard alone function: I enabled trusted source on managed db side, but then cannot add the function to managed db trusted sources.

Does anyone have a solution for this ? thanks