Hi David thanks for posting in the Lucid Community - I'm happy to help! 

To set your default font size simply click your canvas to ensure that no other objects are selected then choose "Auto" from the Font Size menu in the toolbar at the top of the editor. Any subsequent shape you add to your canvas will automatically have "Auto" font size. I've demonstrated this in the GIF below!

I hope this helps! Please let me know if you have any additional questions.

Thank you so much!!

Glad I could help! Please feel free to continue this thread if you have questions in the future. 

This is really helpful thanks!

Hi @soo young a I'm glad! Let us know if we can do anything to support your work. 

Hi, why is it only some text boxes show the ‘auto’ size option in the font size menu? How do I change this so all text boxes have the ‘auto’ option?

Hi @Corinne L, thanks for adding to this thread! Can you please share a temporary Support PIN for this document? This will allow me to take a closer look at the issue you’re experiencing. For more information on generating a Support PIN, check out this Help Center article. I appreciate your help and patience!