The following instructions assume Xcode 13.3 on macOS 12.3.

• Make sure MastodonKit is fetched as a git submodule. (For example, Xcode's git clone functionality seems to not do this!) This appears to be a custom fork called 3.0 that's significantly different from the public MastodonKit. So don't try and pull the regular MastodonKit using CocoaPods.

• You need an Apple Developer ID. In Xcode, head to Signing & Capabilities and set your ID's team.

• QuickToot and Mastonaut need to be in the same team.

• That team ID (the above UI will show it; it looks something like 74J34U3R6X) is hardcoded. Adjust MastonautPersistentContainer.swift accordingly (otherwise, it will build but immediately crash):

class MastonautPersistentContainer: NSPersistentContainer
{
	static let appGroup = "(insert enter your Team ID here).app.mastonaut.mac"

That should be it.