When you Reply or Reply All in new Outlook, the CC line is not visible, even if the message was CC’d to others. The BCC line is also not shown by default on replies when you have the option set to show it in Settings > Mail > Compose and Reply.
In addition, the To line may be truncated and appears to be part of the message body, with your account avatar or photo to the left of the address (and more prominent). It’s difficult to see where the header ends and the message begins as it all blends together, especially because the subject field is not shown within the reply. It doesn't help that the header scrolls, hiding the addresses.
If you want to see the To, CC, and BCC fields, click on the address to show the address fields for editing (including BCC if enabled in Settings). The addresses will have yellow highlighting and you can add or remove addresses. If the field does not show automatically, click the CC or BCC button on the right to show the field. (You can also hover over an address for a few seconds until the contact card comes up then click off the address to enable editing the addresses.)
If you need to add addresses to the CC or BCC field and they aren't showing, click on the CC or BCC text on the right. This will show those fields.
It's a little better if you expand into a new window (the button on the top right in the first screenshot); the To and Subject lines are shown as separate lines, although the addresses are in the same "looks like plain text" format as in the inline reply.
After clicking n the address, you'll see the CC field. If you have the option to always show the BCC field enabled in Settings > Mail > Compose and reply, it will display automatically as well.
