You can use a common data helper object that is synced, there is a sync instance variable action in the multiplayer object.
You can also have the host broadcast the message with the relevant information whenever it changes or when a new player joins, which is what I would recommend, as this variable is not something that needs to be updated 30 times a second.
I like the idea but failed to do it
I tried using using a common obj with an instance variable, I added sync obj and sync var, also the broadcast message to do some tests
1st tried
Host press a button (only visible to host) to convert a boolean to true
that boolean (global boolean) set a random number of 4 digits into the instance variable
text on screen show that instace variable to everyone
results
Host can see the random number and peers see the default text
2st
same example but everyone can press the button
results
everyone see a different value but only when they press the button, i need they to see the same value
im not sure in what im failing, i need a dynmic value that can be changed only by the host when is needed and that value share to all players at same time