The workflow API does not retrieve space workflows at this time.
I spent some time trying to figure out why my space workflows were not being retrieved by the API, then I asked support to find out that space workflows are not yet supported by the API. I thought I would share this in case someone else was running into the same issue.
Tech Support did mention that this feature may be available in 2023 but they were not able to share a target date.
My temporary solution was to make the workflow an account workflow. Not as organized, but it is functional.