Exception:
Your org has too many waiting flow interviews, including processes that are waiting to execute groups of scheduled actions. Wait for some interviews to complete, or delete unneeded interviews.

https://help.salesforce.com/s/articleView?id=sf.process_limits_scheduled_processing.htm&type=5
An org can have up to 50,000 pending schedules and paused flow interviews at one time.

SELECT count() FROM FlowInterview WHERE InterviewStatus = ‘Paused’
It should be less than 50000 to schedule another.