Open it in Chrome
- Save the .mpp file to your Chromebook (Downloads, or Google Drive in the Files app).
- Open the MPP Viewer in Chrome.
- Drag the file from the Files app onto the page, or click the page to choose it.
You get the Gantt chart, the task table with WBS numbers, dates, progress and predecessors, and the resources, free. Nothing to install, no Linux, no Android app.
Make .mpp files open with a double-click
- On the MPP Viewer page, click the install icon at the right end of Chrome's address bar (or the three-dot menu, then Cast, save and share, Install page as app).
- In the Files app, right-click an .mpp file, choose Open with, and pick MPP Viewer.
From then on the plan opens in its own window. ChromeOS may ask once whether the app may open that kind of file.
Other options
Microsoft's web planning tools run in a browser, but they need a paid plan and are built for plans made in them, not for opening an .mpp someone emailed you. Windows in the cloud (Windows 365 or a remote desktop) can run the full Project app, which makes sense for someone building plans all day, not for reading the ones people send you.
Need it in Google Sheets?
The viewer exports the plan to Excel (.xlsx) and CSV, and both open in Google Sheets from Drive. There's also a PDF Gantt chart for sharing. Exports are $19 once for every project you open, with no subscription.