thank you Andrius… I think it works well now. It was not crashing but the mouse cursor was turning to a spinning circle for 30 seconds or more sometimes… I have seen some errors in the DebugView about not being able to generate thumbnails for some .afphoto files… I added that extension in mime type preferences… to try to include those files too. I saw the thumbnail was not supported because it is a closed format, but I saw it listed as a generic icon so I thought it was ok to have them as a link to open with the application maybe… but after removing that extension in preferences… now digiKam seems to be working well so far.
Now I still want to try 7.0 beta, but I don’t want to affect the 6.4 installation or database(using Mariadb). I hope it can be installed in another folder without uninstalling 6.4 and maybe configure it with another database table. Or is it safe to upgrade and use the same database?