Change the text size to above100 pt in powerpoint?

There seems to be a maximum of 96 points in the text size in PPT. In fact you can have a lot more. Just type a larger number in the Font Size box and press enter.

In PowerPoint for Windows you can type a size up to 4000 in the box. In reality, of course, this will be much, much lower.

Text behaviour in a shape - PPT 2019-2021

When you draw a shape and add text to it, it appears by default in the middle of the shape with a size of 18 pt. By default, the behaviour of the text in the shape is set to Do not AutoFit.

Do Not Autofit means the formatting of the text in the shape is not automatically updated.

So, if you adjust the size of the shape, it may happen that the text no longer fits the shape. 

See the video below:

There are two other settings.

The second option Shrink text on overflow shrinks or enlarges the text when you shrink or enlarge the shape.

See the video below:

With the third option Resize shape to fit text, when you adjust the font size or the size of the shape, the shape is adjusted to the text

See the video below: