Studied Film and worked professionally in overdubbing for a while. I recommend in that order:

1. figure out if your mumbling is just a habit or a logopedic issue

2. get a speakers training of the type actors or radio hosts would

If you wonder whether it is worth it, just consider how important it is in both your private and professional life to be clearly understood. There has been a study during the pandemic that showed that people who had the better sound quality in conferences would get their ideas through more often. This is truly the case for spoken words as well.