RE: Insert Email Signature button missing
Hi Lorna,
There is a recent known issue with the 'Attach File' button and 'Insert Signature' button being hidden from the email form.
However, in order to specifically review the issue that you're facing and confirm, I'd suggest to open a Service Request with Microsoft Support.
Below are the workarounds that you could implement for the issues:
1. 'Attach File' button-
'New Attachment' button in ribbon in Attachment Grid is working. You could use this ribbon if you're looking for 'Attach File'.

2. 'Insert Signature' button- You could set one of the signatures as default and then whenever you open a new email, the signature set as default will show up in the email body by default.
-Open the Personalization Settings from here:

-Select 'Email Signature' and open the signature you'd want to keep as default:

- Set the most common signature as default and copy & paste other signatures from Word, Outlook, etc., if required for the time being.
