arimakidd Have made certain changes in configurations in order for iFrame to display :
1) Had made changes as per step5 as the iFrame element could still be seen for element filtering to apply for default editor
2) Changed menu type to single article from iFrame wrapper in order to reflect specific article where iframe script has been added
however, the iFrame script doesnt render neither in default template too even while re-entering the script with codemirror. Ref: Screenshot.
You may get in touch with upwork site support team in order to verify if their iFrame script isnt restrictive to be used elsewhere as also suggested here along with other reasons as stated in specific forum thread or better yet, You may ask them if they have custom javascript code available which can be inserted which is even more convenient