Learn Portuguese (Portugal): Apesar de estar extenuado, estou focado, e sei que tu também o estás. - Despite being drained, I am focused, and I know that you are too.

It is a neuter predicative clitic. Instead of repeating the adjective focado (focused), Portuguese uses o to stand in for the entire idea of "being focused". While English simply drops the adjective and says "you are too", Portuguese requires this o to complete the verb estás.

Why does the pronoun o come before the verb in o estás rather than after it?

The conjunction que (that) and the adverb também (too/also) both act as "magnet words" in European Portuguese. They pull the pronoun to the front of the verb, which is a rule known as proclisis. Without these triggers, the pronoun would attach to the end of the verb.

Why do we use the infinitive estar instead of a conjugated verb like estou after Apesar de?

The phrase Apesar de (Despite) ends with the preposition de, which requires the verb immediately following it to be in the infinitive. Because the subject of both halves of the sentence is the same, we use the personal infinitive estar here rather than switching to a fully conjugated tense.

Is extenuado just another word for cansado?