Saved filters will continue to function using the old project key is correct.

Saved filters will continue to function using the old project key is correct because Jira preserves and updates the underlying references when a project key is changed so queries that reference the project still return the expected issues. Jira stores project references by internal identifiers and it will either update saved JQL or resolve the old key to the project so saved filters keep working after the key change.

Dashboard gadgets that use the project key will need manual updates is incorrect because gadgets that are driven by saved filters or by Jira query references continue to work since the filters and references are updated or resolved automatically. You normally do not have to manually edit each gadget after a project key change.

A new project can be created using the previous project key is incorrect because the old key remains associated for compatibility and redirect purposes and so it is not simply freed up for immediate reuse as a different project key.

Web links that contained the former project key will stop working is incorrect because Jira provides redirects and maintains mappings from old issue keys to the new keys so links that used the former key will continue to reach the correct issues.

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