Drag-select not working in Word

This sounds more like a damaged document, add-in or Word profile than a normal setting. Start by opening a completely blank document and test drag-selection there.

If every document is affected, test Word in Safe Mode:

1. Close Word.
2. Press Win + R, enter winword /safe, and press Enter.
3. Open a document and test drag-selection.

If it works in Safe Mode, disable the add-ins under File > Options > Add-ins. At the bottom, select COM Add-ins > Go, clear the add-ins, and restart Word normally.

If only one document is affected:

1. Open File > Open > Browse.
2. Select the document.
3. Click the arrow beside Open and choose Open and Repair.

The Navigation pane only recognizes paragraphs that use Word’s built-in Heading 1, Heading 2 and similar heading styles. Text that is only bold or enlarged will not appear there. Also check whether the document is in Protected View or has Restrict Editing enabled.

If all documents still fail outside Safe Mode, open Windows Settings > Apps > Installed apps, find Microsoft Office, select Modify, and run Quick Repair. Use Online Repair if Quick Repair does not help.

It is usually caused by input conflicts (mouse/trackpad drivers, add‑ins, or OS updates) rather than a permanent loss of functionality. Would suggest testing in Safe Mode, checking editing options, and verify hardware drivers before contacting Microsoft support.

https://learn.microsoft.com/en-us/answers/questions/5986572/word-wont-select-text-anymore-by-using-mouse-click

Word opens, but drag-selection and the Navigation pane fail, suggesting an add-in, damaged Normal template, or Office installation problem rather than one document. Press Windows+R, run winword /safe, and test a blank document. If selection works in Safe Mode, disable Word and COM add-ins, restart normally, and re-enable them individually. If it still fails, close Word and rename Normal.dotm so Word creates a fresh template; keep the old file. Test another document and confirm headings use Word’s built-in Heading styles, because Navigation does not infer headings from formatting alone. Install Microsoft 365 and Windows updates, then use Settings > Apps > Microsoft 365 > Modify and run Quick Repair, followed by Online Repair if needed. Test a new Windows profile. If every document still fails after Online Repair, capture the Office version and update channel and open Microsoft Support rather than repeatedly reinstalling or deleting registry keys.