@Éric Phénix - Title updated 

@Éric Phénix - You are not missing anything - you cannot have multiple formats in one object, e.g., Text or Shape.

Thanks @Robert Johnson 

@Éric Phénix - You may want to upvote the following Wish List Idea post → Rich text editor

However, if you feel that idea doesn’t truly reflect what you are looking to accomplish, you can post your own Idea in the Wish List category by following the guidelines here: Wish List: Everything You Need to Know.

If you do create a Wish List Idea post, I would also recommend that you post a link to it back here, so that future readers of this post can quickly get to and vote for your Idea.

Lastly, don't forget to vote for your own Idea.

@Éric Phénix -

I’d assume that is by design as I’m getting the same results when I select text and change the size, all text within the text box changes to that size. 

Kiron

Thanks @Robert Johnson, that was exactly it. I add my vote :)

@Éric Phénix If you want to know more about what you can do with text boxes, here's some information with visual examples:

https://help.miro.com/hc/en-us/articles/360017572094-Text

@Henrik Ståhl Appreciated the link but it is all information I’m already aware. My issue is not been able to have different size font in the same text box like Title, normal text, subtext, etc.