Hi @Alois ,
Do you want to hide some items only for current user?
Could you tell me the details of the hiding rule?
Do you have a column with email value and if someone accept activity, this field will update with the person who accept the activity?
Or do you want to hide the accepted activities temporarily when been accepted?
Firstly, I suggest you use Filter function to filter items based on different situations, not set gallery's Visible which will hide the whole gallery.
1)In first situation, you could set gallery's Items like this:
Filter(tablename,Not(status.value = "In Progress" ,'Modified By'.Email = User().Email))
2)In second situation, you could set like this:
set the accept button's OnSelect:
Collect(accepteditems,ThisItem.ID)
set the gallery's Items:
Filter(tablename,Not(ID in accepteditems.ID))
Best regards,