Why-can-t-I-drag-a-Condition-block-to-a-design-surface

You'll have to drop a Condition right on top of an Entry/Exit Block, not on the blank design surface.

Sorry, i didn't know, I'm new. After using 30 years of Metastock it will take some time to ajust me to the new way of working,

30 years! Welcome aboard Henk!
When you have some free time, check out our youtube channel for some tips. The WealthLab 7 videos are worth watching too: https://www.youtube.com/@wealthlab