Users are reporting problems adding addresses to email in Outlook on the web. Microsoft is aware of the issue but I dont have any information on the cause or when it will be fixed.
Some users say it works correctly in Chrome browser and only fails if using Safari.
Update: check for updates for Safari and see if that fixes it.
IMAP Yahoo and AOL accounts might experience issues with re-syncing folder content - Microsoft Support
While we're waiting to find out the cause of the bug and for it to be fixed, you can open the compose message in a new window.
Click the button to pop it out into a new window and you will be able to click in the recipient fields.

Electric_car_charger says
“You’re amazing!”
Druss says
In my case, the paste option does not work either. What a mess.
Diane Poremsky says
The to field should be working now - I'll check and see if paste was fixed.
Yorum Satın Al says
Useful article, thank you. Top article, very helpful.
Tom says
The first few times I tried the above workaround of opening the new mail in its own window, it worked and I could enter email addresses in the TO field. Now these fields in the open window are also unavailable. The only way I can add the recipients now is to first save the recipient as a contact in my address book. Then I can click on the TO button and find the contact. Very inefficient and I hope it is solved soon. Any other ideas?
Vivian says
Still not working - is this permanent now? Very annoying. Do you know if they are working on it? thank you.
Diane Poremsky says
Microsoft knows about it - I don't know the status - if it will be fixed or when, sorry.
Vivian says
Thanks for responding - it just seems so basic - and so frustrating!!
Vivian says
Its working again!! 5/8/23! Hope it lasts!!
Reena says
You can also click on To button, it displays the list of all contacts
Craig says
Great workaround - thank you very much
Nandita says
It doesn't work on Safari but the trick works - open new window. Thank you so much
christine johnson says
Thank you for the problem solve. I wish they would update the program.
anna says
thank you so much. I thought i was going crazy.
J. R. says
Had issues on Safari for days. Firefox works fine. Thanks.
John Murdoch says
VERY HELPFUL, thank you for the workaround
lawrence besseling says
this worked excellent. thank you for the pointer.
James Oldershaw says
Confirmed on Safari - but on same computer Edge and Chrome are fine.
User reported lag on Chrome though which is why they were using Safari.
Cheryl Dunham says
This is incredibly helpful, while not ideal it works and that is great news!
Vivian says
Would be grateful to know when this is solved. Works fine on Firefox but not on Safari.
Vivian says
thanks for the solution - would be grateful to know when its fixed - as above, works on Firefox, but not on Safari.