Mask to expose object

if you use shape tweens you can animate that just as if it were being written.

Hi.

One ease way would be to create a rectangular mask and animate if from left to right to reveal the letter.

To create a mask, you must create an instance (shape, bitmap or symbol instance) in a layer above the content that needs to be masked, right-click the layer that contains the mask content and choose Mask.

More details here:
https://helpx.adobe.com/animate/using/using-mask-layers.html

Regards,

JC