The process of combining the Meet and Duo apps is so complex that it's copying a feature from the Zoom app. You will soon be able to unmute yourself by holding down the spacebar and releasing it, thanks to a new feature in the upcoming version of Google Meet.
This feature is similar to the push-to-talk feature in that it sounds like it. Whenever you want to chime in during a meeting but don't want to stay unmuted for long, you can use the feature at zoom.
It could take up to 15 days for you to see the new version of the shortcut that will be rolled out by Google. It won't be turned on by default, so you'll have to enable it from the settings.
The old Meet app, the Duo shortcut, and the new Meet app are the only things left after the merger of Duo and Meet. Only one person could think up something like that. I am pretty sure that the new push-to-talk feature is coming to the new Meet app, but I am not sure if it is coming to the original Meet app. The Verge tried to clear up the situation, but didn't hear back.