Do you see the indent indicator (on the ruler) moving properly, or does it "snap back" into the original position after you release the mouse button? In that case, try holding the Alt key while you drag it. This should give you the ability to fine-tune the position of the indent.

Also, indentation applies to a whole paragraph, and/or to its first line of text, which is why selecting part of a paragraph shouldn't make a difference.

Are you sure that your paragraphs start and end where you think? Display nonprinting marks, including paragraph marks (¶) by clicking the ¶ button on the Home tab.

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Stefan Blom
Microsoft Word MVP

Microsoft 365 apps for business
Windows 11 Professional