Recently released to Project for the web is the Critical Path view for users with P3 and P5 licenses, this enables you to easily see which tasks impact the project end date. This can be seen below on my test project:
This feature is available on the Timeline view by clicking the Filter option as seen below:
Use the “Show Critical Path” toggle option to show / hide the Critical Path for the project.
Another great addition to Project for the web.
Modern Work Management - Project and the Power Platform blog 