Dear loobO(2)
Thank you for posting to Microsoft Community
I understand that when you use Ghrome on your Mac to view or compose a new email, the text area you see is enlarged. And the zoom you set on Ghrome is still 100%. I do understand your frustration.
Please move your mouse over the text area, hold down Ctrl + mouse wheel and try to reduce the size of the text area.
Let me know how it goes and I'll be here to help you further if needed!
I wish you all the best
Linda.W-MSFT | Microsoft Community Support Specialist