"All instances" will only be enabled when there are more than one instance of the selected delimiter text in the sample value. In your case you selected "sktop Suppl" which only occurs once. If you select a space, "All instances" is enabled and you can select to split on all spaces.
I'm having the same issue using Sense Desktop November 2018 Patch 2. I'm following along with the Qlik training module for Split and in the video the 'These Positions' option is available, however, it's grayed out for me. Can only choose 'This Instance'.