Learn Spanish (Latin America): Estudio mucho para que mi español sea fluido. - I study a lot so that my Spanish is fluent.

The phrase para que (meaning "so that" or "in order that") always requires the subjunctive mood. It expresses a goal or an intended outcome rather than a stated fact. That is why we use sea, the subjunctive form of ser.

Can I just say para mi español es fluido?

No, because the subject changes in the middle of the sentence. The person studying is "I", but the subject of the second half is "my Spanish". When the subject changes to express a goal, you must use para que plus the subjunctive. If the subject remained the same, you would use para plus an infinitive (for example: Estudio mucho para ser fluido).

Why do we use a form of ser (sea) instead of estar (esté)?

We use ser because being fluent is considered a defining characteristic or long-term quality of your Spanish skills, not a temporary condition or location.

Does fluido change depending on the gender of the speaker?

No, fluido is an adjective that describes the noun español (which is masculine and singular). It does not change based on whether the person speaking or studying is male or female.