You can't remove all style and format - despite what the Word GUI misleadingly says. There is ALWAYS a Paragraph Style applied and that style has formatting associated with it.
However, you can remove local formatting and apply a 'default' style called Normal via a command either called "Clear Formatting" or 'Clear All' - see
Remove Styles from Text in Word - Instructions - TeachUcomp, Inc.
Ctrl-Space removes local font formatting including Character Style (if there was one) but it doesn't change the paragraph style applied. Ctrl-Q removes local paragraph formatting and doesn't change the paragraph style.