You can use MetadataComponentDependency (Beta) object. It has dependency maintained. You can query for dependency.
Link for the documentation -
Well, in thinking further about the WHERE clause specifically causing the issue, I wondered if it was a spacing issue. I edited that line to remove spaces in the SELECT and WHERE:
SELECT Id,FlowVersionId FROM FlowElementTestCoverage WHERE FlowVersionId=\'[myFlowVersionId]\' LIMIT 1'
...and it worked!