Learn Dutch: U kunt deze regel overal toepassen. - You can apply this rule everywhere.

Because it is used with the modal verb kunt (can). When a separable verb is the main infinitive in a sentence with a modal verb, it stays together as one word and is placed at the very end of the sentence. It only separates when it acts as the conjugated verb, like in: Ik pas de regel overal toe (I apply the rule everywhere).

Since u is the formal 'you', shouldn't the verb be kan (like he/she/it) instead of kunt?

For the formal pronoun u, both u kunt and u kan are actually correct! However, u kunt is strongly preferred in written and polite Dutch, making it the safest choice to match the formal tone of u.

Could I put overal at the beginning of the sentence to emphasize it?

Yes, you can! Just remember that putting an adverb at the start triggers verb-second (V2) inversion. The verb must stay in the second position, meaning the subject (u) and verb (kunt) will swap places: Overal kunt u deze regel toepassen.

Why is it deze regel and not dit regel?