If you're still seeing the old Exchange Log On window, then Modern Authentication is not enabled/configured correctly in GP.
To verify, are you able to successfully email either of the following, seeing the 'Sign In To Your Account' windows and not 'Exchange Log On'?
>> Financial Trial Balance
1. Click on Financial > Reports > Trial Balance
2. In the report window that opens, select a report such as 'Summary' and then highlight the report option such as 'demo' and click Modify.
3. In the report options window, click the 'E-mail Options' button and it should prompt with the 'Sign in to your account' windows for your modern auth credentials.
4. In the email options window that will open after authentication is successful, add your email address in the TO: field. Click OK to save changes.
5. Back in the report options window, select that option again that you just did setup for and then click the 'Email' button in the menu. You should see a Progress/Generating Email window before you receive the email and report attachment.
The sending email address should be the Exchange credentials entered when prompted in step #4 above.
>> User Notes report
1. Click on Administration > Reports > System > Users
2. In the User Reports window that opens, click 'New...', unless you already have a report option available for use. If you do, jump to step #6.
3. In the report options window, name the option and then choose a range of user(s) to put into the report and click Insert. Save changes.
4. Bring up this same report option created and click the 'Email Options' button at the bottom right-hand side of the window.
**NOTE: You may be presented for your credentials via the 'Sign in to your account' windows, if you haven't already entered them in this GP session.**
5. In the 'Email Options' window, put your email address in the 'TO...' field, to send the email to, click OK to save changes. Close the User Report Options window.
6. Back in the User Reports window, select this report option and click Insert.
7. Highlight this report option and click the 'Email' button in the menu across the top of this window. You may briefly see a progress window open and close.
8. Verify you receive this email that was just sent. It may take a couple of minutes.
If you cannot email either of these two reports or you're still seeing 'Exchange Log On' windows, then Modern Auth is not configured correctly, and you'll want to double-check that setup.
Thanks