Hi Elncl,
Thanks for reaching out to Apple Support Communities. It sounds like you're having an issue with Messages on your Apple Watch. We're happy to provide some information to assist.
The option to compose a message using dictation is still available with watchOS 8. The guide here has details: Send messages from Apple Watch Specifically, the section "Compose a text message" which states:
Dictate text: Tap
Say what you want to say, then tap Done. You can speak punctuation, too—for example, “did it arrive question mark.” say what you want to say, then tap Done. You can speak punctuation, too—for example, “did it arrive question mark.”
If the issue continues, complete a normal restart of your iPhone and Apple Watch and test. If needed, the steps below will help.
Restart your Apple Watch
Restart your iPhone
Best!