Dear Alex Moonin,
Good day! Thank you for posting your query in our community.
Per your description, you mentioned "MS Project Web Based", may I confirm whether you mean the Project for the web?
If yes, from this official article: Project for the web and Project Online desktop client - Microsoft Support, we can know that the Import from Excel feature is not available for Project for the web.
If my understanding is wrong, please feel free to post back and correct me.
Sincerely,
Jazlyn | Microsoft Community Moderator