When using the Explore tool ArcGIS Pro to identify attributes for a feature, the pop-up window is only showing one of the fields within that feature class. I have even tried "Configure Pop-ups" to see if that would work and nothing changed. Is this a Bug with ArcGIS Pro 2.6?
I too have observed this after upgrading to ArcPro 2.6 when opening Projects created prior to ArcPro 2.6. When adding new layers in 2.6 Explore tool shows "all available" attributes - but exisitng layers only show the default label field attribute. This is without setting up Popups which I typically avoid on my own data manipulation Projects (not that setting them up on the old layers helps)
Please see the below link, which is where Robert provided me with a solution.
Hope it helps.
Elizabeth/Todd - to solve this move your mouse to the bottom of the Pop-up. Your mouse cursor will change to an up/down arrow, click and hold your left mouse key and move the lower (collapsed) portion of the pane to the mid-point of the pop-up. Now you will see all the attributes as expected. Click on Cheryl's link above for the other Esri Community post addressing this same issue.