Disable Keyboard Interaction with UIHostingController. https://steipete.com/posts/disabling-keyboard-avoidance-in-swiftui-uihostingcontroller/

UIHostingController-Keyboard.swift

extension UIHostingController {
    convenience public init(rootView: Content, ignoreSafeArea: Bool) {
        self.init(rootView: rootView)

        if ignoreSafeArea {
            disableSafeArea()
        }
    }

    func disableSafeArea() {
        guard let viewClass = object_getClass(view) else { return }

        let viewSubclassName = String(cString: class_getName(viewClass)).appending("_IgnoreSafeArea")
        if let viewSubclass = NSClassFromString(viewSubclassName) {
            object_setClass(view, viewSubclass)
        }
        else {
            guard let viewClassNameUtf8 = (viewSubclassName as NSString).utf8String else { return }
            guard let viewSubclass = objc_allocateClassPair(viewClass, viewClassNameUtf8, 0) else { return }

            if let method = class_getInstanceMethod(UIView.self, #selector(getter: UIView.safeAreaInsets)) {
                let safeAreaInsets: @convention(block) (AnyObject) -> UIEdgeInsets = { _ in
                    return .zero
                }
                class_addMethod(viewSubclass, #selector(getter: UIView.safeAreaInsets), imp_implementationWithBlock(safeAreaInsets), method_getTypeEncoding(method))
            }

            if let method2 = class_getInstanceMethod(viewClass, NSSelectorFromString("keyboardWillShowWithNotification:")) {
                let keyboardWillShow: @convention(block) (AnyObject, AnyObject) -> Void = { _, _ in }
                class_addMethod(viewSubclass, NSSelectorFromString("keyboardWillShowWithNotification:"), imp_implementationWithBlock(keyboardWillShow), method_getTypeEncoding(method2))
            }

            objc_registerClassPair(viewSubclass)
            object_setClass(view, viewSubclass)
        }
    }
}

I just learned that since iOS 16.4 this is no longer needed. You can now use self.safeAreaRegions.remove(.keyboard): https://developer.apple.com/documentation/swiftui/uihostingcontroller/safearearegions