If you are unable to edit your campaign, please check if you are using the Classic Designer.
If you are, please create your campaign in the Email Designer (launched in 2022) which does not have this issue.
To ensure you are using the Email Designer (launched 2022), when creating a new campaign or template, select the "Email Designer" option on the “Choose a Template Type” modal:
If this does not solve the issue for you, contact our Customer Experience Team, and we’ll be happy to look into this further.