You need to cast to the correct reference of your hud widget blueprint, some things you need to do.
get a reference to your hud blueprint into your “mode” blueprint, you can get this from where you add your widget to the viewport for example, (the return node on the “create widget” node you used is a reference to that specific version of the spawned widget blueprint - thats what we need).
drag out a node from said widget reference then “cast” to that type of blueprint, make sure you aren casting to any of the generic types - I would recommend using a more specific name for your hud widget to remove any confusion here, “in_game_hud” or something.
drag from the cast to run your/any event in the cast blueprint.
// hope that helped, glhf