There is not a native way to do this. But you can produce the results you need by replacing your text field with multiple overlapping formula fields that conditionally display that text in that field depending on its number of characters, and having each of those overlapping fields have a different font size.
Here’s an example for how to make the formula fields:
IF(
AND(
LEN({Your Text Field})>=11,
LEN({Your Text Field})<=20
),
{Your Text Field}
)
This version would only show your text if it is between 11 and 20 characters. Make more of these formulas, changing the numbers as needed, and create as many break points as you need for your overlapping fields in the page designer. Tweak the character break points and the font sizes until you get whatever combination works for your needs.
It’s not the most beautiful solution, but it does work.