The correct form is braver.
To understand why, we need to look at how we use comparative adjectives in English. The word ‘brave’ is an adjective that describes someone who shows courage. When we want to compare the bravery of two or more people, we need to use the comparative form of the adjective.
In English, most one-syllable adjectives form their comparative by adding ‘-er’ to the end. Thus, ‘brave’ becomes ‘braver’. For example, we might say, ‘She is braver than her brother.’ This clearly indicates a comparison in bravery between the two individuals.
On the other hand, ‘more brave’ can be understood but is less commonly used and can even sound awkward to native speakers. It is often best to stick with the correct comparative form ‘braver’ for clarity and grammatical accuracy.