Hey, is there a way to instantly force the execution of a PrefectSecret task and set it with no upstream ?

Yes

with Flow(...)
    PrefectSecret("Something")()

Yes, there is! You can invoke it from your local Python script using e.g.:

from prefect.tasks.secrets import PrefectSecret

print(PrefectSecret("A_PASSWORD_DEV").run())

You may need to set this env variable beforehand:

export PREFECT__CLOUD__USE_LOCAL_SECRETS=false