When you use ArcGIS Online Experience builder you can add action triggers to make your map frames react to actions performed on another frame. This allows you to link extents and things.
The problem is that they never added a scroll bar, so once you get past 21 data sources (at my screens native resolution) you can no longer select them as the trigger source. (I'm using this platform to display multiple days of data in 2D and 3D side by side and have about 35 currently)
My current work around is to set the display resolution to a high value, then set the display to portrait rather than landscape which makes the rest of the data sources appear as the window stretches out after physically rotating my monitor. This is fine for now but I'll have the same issue when I hit about 45 as I won't be able to scroll or select them again when the window fills up.
I would add a picture of the issue but it won't let me upload right now... but basically it seems that someone just forgot to add a scroll bar.