Support for Migration derivers ?

I am surprised this didn't get any attention in a year or so...

Same issue here - spent several hours on it and it appears Migrate Plus configurations do not support derivatives. Worth noting that it also appears Migrate Plus configurations are derivatives themselves. I end up writing standard migrations for some of the content I need to migrate.

I know this an older issue, but I ran into this recently and wanted to document my solution in case anyone else runs into this.

This is what solved it for me: I added the migration to my custom module's /migrations folder prior to enabling the module. I am guessing core's migration discovery discovers the deriver this way.
Because now the config gets created, without deleting the deriver parameter.

This was also good post for me: https://www.webomelette.com/dynamic-migrations-using-templates-drupal-8