The useful starting point
A subject such as Update says little about whether a reader needs to decide, review or simply keep a note. A more useful label can identify the project, topic and requested action. Avoid suggesting urgency that the message does not actually justify.
A small step to try
Write the message first, then check the subject against its contents. Remove a request for approval if no approval is needed. When a thread changes topic, consider whether its old label still fits. This is a writing exercise rather than a promise about response rates. The goal is to help the reader predict what they will find before opening the message.