You can call those game instance functions from places like the character blueprint or the player state and others without having to run anything on the server and have them occur locally but also be happening on everyone.
If you need it to occur at specific times within gameplay like a team scoring against another team and a widget appears on everyone saying the other team scored, you can call if from the game state as a server event that multicasts to an event on the player states to the game instance in that particular situation.
If it just needs to show up when the game starts you can pretty well just cast to the game instance and run those events off begin play, but just need to make sure it’s not running on the server and throwing errors by using switch has authority and bypassing anything that’s trying to add widgets to the viewport on the server.