Field [event.ingested] of type [keyword] does not support custom formats

I am using elasticsearch 7.10. On Friday night, one of the indices threw the error llegal_argument_exception at shard 0index xx.yynode FNZgMx35SGBsn8a1rs0WKQ Field [event.ingested] of type [keyword] does not support custom formats

How do I solve this?

elasticsearch 7.10 is EOL and no longer supported. Please upgrade ASAP.

(This is an automated response from your friendly Elastic bot. Please report this post if you have any suggestions or concerns :elasticheart: )