If it is possible to reload a SwiftUI widget from an Objective-C main app Sure. You can define a Swift class, and put your reload methods there. Dont forget to add @objc attribute to the function.
import WidgetKit
class WidgetContentLoader: NSObject {
@objc public static func reloadWidgetContent() {
WidgetCenter.shared.reloadTimelines(ofKind:..)
}
}
Now you can call the function in the Objective-C file.
[WidgetContentLoader reloadWidgetContent];