For other who may be struggling with this, please note:
My development system is at the current release level 19.4.0.38 (Volume 4 2021 - December 17, 2021)
However I could not get the required functionality to work on current release level.
I found the last level where BOTH
(a) summary values are updated automatically without a grid refresh
and
(b) the Target attribute is supported by the spinner control
was at Release 19.1.0.64