1. When you paste in plain text (Text only) format, the text takes on the formatting at the insertion point. In which way isn't this working for you? What do you expect to happen?

Also, which style default did you try to change? And which option, specifically, was greyed out?

2. In the Styles pane (Ctrl+Shift+Alt+S), right-click the styles you want to get rid of and choose Delete from the context menu. Note that this only works with custom styles (built-in styles can't be permanently deleted).

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Stefan Blom
Microsoft Word MVP

Microsoft 365 apps for business
Windows 11 Professional