There is a known bug in Word that prevents users from resizing shapes and text boxes with drag & drop. Microsoft is investigating this but it isn't yet known when we can expect a fix.

As a workaround, you can use the controls on the ribbon to modify the objects. Or you can convert the document to the most recent *.docx format.

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Stefan Blom
Microsoft Word MVP

Microsoft 365 apps for business
Windows 11 Professional