[SOLVED] Question regarding Checklists

So there's hope however, I've tried to follow your guideline but I don't get it.
I hope you'll have a little patience with me. I did the following according to your second suggestion and I did it in 2 different ways:
First: I create a new Activity, linked it to a sub-project, saved it but it disappears right away and turns out to be closed right away. Can make it visible by selecting the Show Closed Items check mark. It does not appear as a linked item on the specific project page.

Second: Created a new linked element from the project page. selected Activity Type. Clicked the Search next to the "linked element" edit box which brings me to the Item list detail window which is empty. Click the Create new item button which gives me the same input screen as in the First attempt. So I've created a new activity and saved it. Now the activity is there as a linked element but I cannot figure out how get a checklist linked to this activity. Again the activity only shows up again as a closed item in the Activity window. If I follow the link from the project page clicking the linked element the Activity is shown but also states it's closed today(?).

I'll try that but it still does not explain why the Activity is closed right after creation...

It's version 5.3.3
Looks like something is going wrong indeed.
Whether I use "Decision" or "Activity" it doesn't matter. They all are marked as "Done" right after creation.