I am unable to compose email on my imac

This may appear the be insulting and that is not the intent

But have you added an e-mail to the computer ?

Add email accounts in Mail on Mac - Apple Support (CA)

Welcome

After though.

Are you attempting to use Hand Off between your computer and iPad /

For additional reading on this subject

refer to link below

Use Handoff to continue tasks on your other devices - Apple Support (CA)

Ford1985 wrote:

Why cant I compose email on my Imac?

What happens when you try?

What MacOS version?

Details and context will help us help you.

Writing an effective Apple Support Commun… - Apple Community

To be truthful - I can not put my finger on " the why " this would happen nor what has been done to make this change

Any time I start a New e-mail on any of the four different Apple Computers ( 3 with Ventura and 1 with High Sierra ) and place the Curser in the To Field, the vertical Curser will flash on and off

Once I start to type the Recipients Name or part of their e-mail address = presto the field will fill

Perhaps a Voice Conversation to Apple Support may or may not prove more fruitful ?

Get Support Choose a product and we’ll find you the best solution.Start now and open an Apple Support Ticket as they are Apple Employees to deal will these types of issues . 

So, is the User ( you ) saying.

You have Clicked in the " To " field and it does not allow you to input an e-mail address ?

Or something else happens ?