Übergangsblenden in Adobe Premiere Elements für Mac

Do you mean dissolve transitions are not working?

Did you try pressing Enter to render the timeline?

Do you have enough handles?

This is for Premiere Pro, but the same principles apply for Premiere Elements:

https://www.mediacollege.com/adobe/premiere/pro/transition/handles.html

Where are you seeing aperture templates in Premiere Elements? Which effect uses them?

This may be difficult to answer because I'm using the computer translations.  

You didn't say which version of Premiere Elements you are using.  In some later versions, certain parts are not installed until actually used.  This is to prevent wasting space on your drive.  In the very latest versions some of the tranistions need a GPU and may not work without it.   

So that I can try understanding, perhaps you could post some screen shots of where you are having trouble. 

Das würde ich jetzt aber nicht im Stock Contributor Forum posten. Ich werden den Beitrag in das richtige Forum verschieben. Viel Glück mit den Antworten.