The upper altitude is 66,560ft MSL. The middle altitude is 65,958ft AGL. Presumably, the terrain rises to 602ft MSL in that location.
The bottom altitude is 19,494m MSL, which converts to 63,956ft MSL. Note that this is GPS altitude, whereas the other two should be pressure altitude when up this high, so it is natural that they disagree by quite a bit.
Also, the two displays on the right show 66,569ft and 66,430ft. The former agrees with the MSL at the top of the main display, as I’d expect. The latter does not appear to be within tolerance and should be tested/calibrated, though perhaps the pilot just forgot to change it to pressure altitude.