What is the difference between Quick Filter and Normal filter?

They are the same filter. The difference is whether the reader can see and change it.

A normal filter sits on the Filters shelf and applies silently. Only someone editing the workbook can alter it.

A quick filter is that filter with Show Filter turned on, so it renders as a control — a list, dropdown, slider or search box — that a reader can operate.

The practical consequence is cost rather than logic. Every quick filter is rendered and, if set to Only Relevant Values, runs an extra query to work out which values still apply. A dashboard with a dozen quick filters on high-cardinality dimensions will feel slow for that reason alone.