EntityQuery where multi-value field contains a value

I've been programming for 15 years, 10 with PHP, but on my 1st Drupal project. Using Drupal 9.

I'm trying to retrieve an entity (custom content type) that has 2 multi-value entity (user) fields. If the value I have is in one field I want to get the other one. The problem is I can't figure out how to ask for the entity when the scalar value I have is in the list. Here's what I've got:

return \Drupal::entityQuery('node')
  ->condition('type', 'osj_relationships')
  ->condition('field_supervised_reps', [$userId], 'IN')
  ->execute();

Which generates this SQL:

'SELECT "base_table"."vid" AS "vid", "base_table"."nid" AS "nid"
FROM
"node" "base_table"
INNER JOIN "node_field_data" "node_field_data" ON "node_field_data"."nid" = "base_table"."nid"
INNER JOIN "node__field_supervised_reps" "node__field_supervised_reps" ON "node__field_supervised_reps"."entity_id" = "base_table"."nid"
WHERE ("node_field_data"."type" = 'osj_relationships') AND ("node__field_supervised_reps"."field_supervised_reps_target_id" IN ('2458'))'

The 2nd part of the WHERE clause is looking for the field value in my parameter. I need it to look for my parameter in the field. I've also tried CONTAINS but that seems to assume the field value is a string rather than an array. If I could turn that WHERE clause around it would be perfect. ie.

(('2458') IN "node__field_supervised_reps"."field_supervised_reps_target_id") 

I suppose I could use 'CONTAINS' if I could implode the field list but that would risk false hits.

Any suggestions?

You don't even have to use IN here, only if you have multiple $userIds, otherwise a simple = operator will work:

return \Drupal::entityQuery('node')
  ->condition('type', 'osj_relationships')
  ->condition('field_supervised_reps', $userId)
  ->execute();

The generated query will actually work how you'd like. It works because each value of a multi-value field is stored in its own row in the database.

For example, given a multi-value entity reference field, field_tags, added to article nodes, if you have an article (with id = 111), referencing two taxonomy terms with ids 222 and 333, the node__field_tags table might look like: