Learn Spanish (Latin America): Los movimientos, los cuales fluyen bien, son hermosos. - The movements, which flow well, are beautiful.

You can absolutely use que here, and it is much more common in everyday speech. However, in formal writing or speech, forms of el cual (like los cuales) are often used to introduce non-defining relative clauses—the extra information tucked between commas. Notice that los cuales has to match the gender and number of the noun it refers to, los movimientos.

What happens if I remove the commas around los cuales fluyen bien?

If you remove the commas, the grammar breaks. Forms of el cual cannot be used as the subject of a defining relative clause (a clause without commas that restricts or defines exactly which specific things you mean). Without commas, you would have to say Los movimientos que fluyen bien son hermosos.

Could I use los que or quienes instead of los cuales in this sentence?

You cannot use quienes because it only refers to people. You also shouldn't use los que here; while los que is used after prepositions, using it as a subject in a non-defining relative clause (between commas) is generally considered clunky or incorrect in standard Spanish. Stick to que for everyday use, or los cuales for formal situations.

Why is the verb fluyen spelled with a "y"?