If you don’t, Shotcut will automatically resize the text to fit the entire width (or height) of the text container (rectangle control).
So, depending on the number of characters you write, the font size will vary.
To replicate the same effects (popping, movements etc…) is possible with Shotcut, but it would take a lot of editing work. That guy probably have built-in effects or presets his video editor that makes the process easier.