Thanks everyone! I was able to answer my own question using the links and a bit of creativity.
So I don't think you can get a list of workflows at the site level, but I was able to do it by runnin two API calls using Power Automate:
- The first SharePoint HTTP GET call gathers all the lists on my site: https://[server]/[sitecollection]/[site]/_api/web/lists/
- A second SharePoint HTTP GET call loops through each list and gathers all the associated workflows: https://[server]/[sitecollection]/[site]/_api/web/lists/getByTitle('[ListTitle]')/WorkflowAssociations
It even told me whether the workflow runs manually, automatically on created, or automatically on modified.