How do I upgrade Graylog from version 4.3 to 6.x?

Currently, I am using Graylog 4.3, MongoDB 4.4.17, and Elasticsearch 7.10.2.

The maximum MongoDB version supported by Graylog 4.3 is 5.0, while the minimum MongoDB version required by Graylog 6.x seems to be 5.0.7.

In this case, should I upgrade MongoDB to version 5.0 first, then upgrade Graylog to version 5.x, and afterward, upgrade MongoDB to version 5.0.7 or higher before upgrading Graylog to 6.x?

Does Graylog 4.3 not support MongoDB version 5.0.7?

Thank you.

After upgrading to Graylog 6.1, the following error occurs when running it. What could be the issue?

Loading component failed: Cannot read properties of undefined (reading ‘variant’)

2025-01-03T17:41:26.200+09:00 ERROR [NotificationSystemEventPublisher]
java.lang.IllegalStateException: System notification event definition not found
at org.graylog2.notifications.NotificationSystemEventPublisher.lambda$publish$1(NotificationSystemEventPublisher.java:144) ~[graylog.jar:?]
at java.base/java.util.Optional.orElseThrow(Optional.java:403) ~[?:?]
at org.graylog2.notifications.NotificationSystemEventPublisher.publish(NotificationSystemEventPublisher.java:144) ~[graylog.jar:?]
at org.graylog2.notifications.NotificationSystemEventPublisher.run(NotificationSystemEventPublisher.java:112) ~[graylog.jar:?]
at com.google.common.util.concurrent.AbstractExecutionThreadService$1.lambda$doStart$1(AbstractExecutionThreadService.java:57) ~[graylog.jar:?]
at com.google.common.util.concurrent.Callables.lambda$threadRenaming$3(Callables.java:105) ~[graylog.jar:?]
at java.base/java.lang.Thread.run(Thread.java:840) [?:?]