I despise Cameron for the whole referendum mess, but I can see that appointing him would not be a stupid idea. One of the main defects with Sunak's cabinet has been lack of experience, including lack of experience in opposition, because Johnson basically got rid of all the ministers with any sense. This begins to remedy it, and it's particularly important to have someone experienced in the FO currently.
Plus it's pleasing that Sunak hasn't been stupid enough to promote Jenrick.
BBC are suggesting that Braverman was sacked from the government outright because she made it clear she wouldn't accept a more junior post. No surprises there.