The Realtime_DB block has been replaced by cloud variables. I would recommend using those as explained in the documentation.
This topic has some examples of what those cloud variables look like: From where can we get the realtime DB block in new thunkable? - #2 by tatiang
If you can write to the Firebase realtime database then you should use cloud variables to read from it. Also, before you work on an alert, make sure you can set a label’s text to a simple value from your realtime database. What is the green value block’s value from your screenshot? And the object properties of value?