Task REST-API filter standalone tasks

Hi Camunda-Team!

I’m trying to receive a list of all existing standalone tasks (tasks which have either been created over the tasklist function “Create task” or by API) using the REST-API (POST /task).

Does anyone have an idea how this can be accomplished?
Standalone tasks differ from regular process tasks e.g. by not belonging to a definition or not having an execution.
However filtering for the absence of a definition or execution by posting something like this:

{
 "processDefinitionId": null,
 "executionId": null
}

does not seem to do the job.
Instead, the filter is ignored and always all tasks are returned including the regular process tasks.

Am I missing something or is it actually not possible to build a query with such filter arguments?

best regards,

Chris