Correct spelling, explanation: the correct form is more so. More so is used to indicate that a particular quality or statement applies to a greater extent in one situation compared to another. It’s an adverbial phrase that emphasizes a degree or extent. Moreso is not considered a standard spelling and is generally considered incorrect. The correct form to use is more so when expressing the idea of a greater extent or emphasis.

Definition of more so:
phrase, to a greater extent or degree
She loved the city for its vibrant culture, but what she admired, even more, was the warmth and friendliness of its people, making her enjoy her stay even more so.
Exercise is important for everyone, but for athletes, maintaining proper hydration becomes even more crucial during intense training sessions, as they sweat more and lose fluids more rapidly.

Collocations with more so:
Some most commonly used collocations include:
1. Even more so: used to emphasize a statement and indicate that a particular quality or condition is true to an even greater extent.
The movie was enjoyable, but the unexpected plot twist in the end made it even more so.
2. More so than: used to compare two things and emphasize that one of them possesses a particular quality to a greater degree than the other.
He enjoys hiking more so than any other outdoor activity because it allows him to connect with nature.
3. More so for: used to emphasize that a particular situation, circumstance, or quality applies especially to a specific group of people.
Learning a new language can be rewarding for anyone, but it’s even more so for those who love to travel.
4. More so now: used to indicate that a statement is particularly true or relevant in the current or present context.
With the pandemic, the importance of staying connected with loved ones is more so now than ever before.

Incorrect spelling, explanation: while moreso might seem like a plausible spelling, it’s not considered a standard or correct form in English. The correct spelling is more so. English spelling can be quite intricate, and some words or phrases might appear intuitive or logical in one form, but they follow established patterns and conventions that dictate their proper spelling. More so is the accepted and recognized way to write a phrase that indicates a greater extent, emphasis, or comparison.