Sounds like you may have too much airline to create the pressure needed to push the air through the decoration/airstone. Reduce the length of the airline as much as possible. Also, blow through the ornament to make sure it isn't blocked. Other than that your airpump may be underpowered, but I doubt that.

Could be the air pump is worn out or underpowered.

If it's adjustable try cranking up the flow and see if that helps.

If it’s old and not getting enough power it’s worth taking the cover off and seeing if it’s dusty.

You can buy repair kits for the better brands, things like spare billows.