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

Also, check the following link for additional troubleshooting

https://trailblazer.salesforce.com/issues_view?id=a1p4V0000003z6IQAQ&title=interviewstatus-error-ignores-the-records-with-null-interviewstatus-which-is-affecting-the-paused-flow-interview-limit-check