Data Lifecycle Manager

A "CreateSnapshot" event is output to CloudTrail.
You can check this to see if it has failed or succeeded.

As described in the following document, there is also a CloudWatch metric called "SnapshotsCreateFailed" that can be used to check the number of failed attempts.
https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/monitor-dlm-cw-metrics.html#metrics

It is also possible to use "Event Bridge" to be notified when a "CreateSnapshot" event occurs.