Weird MS Word behaviour

Not an unusual subject line, perhaps!

Mac Mini, M1, Big Sur. Office 365, fully updated (Word updated 13th April).

Dragging with the mouse to select text has stopped working. Click works; so do double- and triple-click. Shift-click works. Shift-arrow key to select works, as do shift-option- and shift-command-arrow key. But click-and-drag with the mouse just leaves the cursor at the “mouse-up” location.

It happens only in Word: not in Finder, nor in TextEdit, for example, but in all Word documents and in all views.

Any ideas gratefully received!

Check Word’s preferences to make sure nothing got changed by mistake. In particular, I’m thinking of Edit > Drag-and-drop Text Editing. I normally keep this off, but when it’s on, you can drag a selection to move the selected text. It might be interfering with drag-based selection.