A filename in File Explorer is not proof that the file's contents are stored on the laptop. OneDrive Files On-Demand can show online-only items that need a connection before they will open. Check important material before travel, a site visit or leaving a computer without network access.

Start with the actual work you need to do. A presentation may depend on linked videos, a project on reference documents, and a spreadsheet on separate source files. Select the complete working set rather than only its main document. Check that the laptop has room for those downloads.

Download deliberately

In your OneDrive folder, right-click the required files or folder and choose Always keep on this device. Allow downloads to finish while the connection is stable. Microsoft's status indicator for always-available items is a green circle with a white check. Read any sync errors instead of assuming elapsed time means completion.

Choosing an entire folder also makes new files added within that folder download as always-available content. That is convenient for a small project, but selecting a very large archive can consume more storage than intended. Use a focused folder or individual selections when capacity is limited.

Perform a realistic offline check

Close the relevant applications, temporarily disconnect from the network and open the exact files you plan to use. Check embedded or linked material too. A successful file download does not guarantee that an application requiring online sign-in or an external service will work offline.

Reconnect after the test. If you edit during the rehearsal, allow those changes to sync and check for conflicts before continuing on another device.

When the trip or job is finished, use OneDrive's Free up space option if you want those files to become online-only again. Deleting a synced file is a different action and can remove it from OneDrive elsewhere. Offline availability is useful preparation, but maintain a separate recovery plan for documents you cannot afford to lose.

Reference: Microsoft Support.