Before I can select the preferred theme but now the theme icon is on the obsolete
Welcome to the forum @Mo.Saleh
You need to write or paste something in order for your post to make sense.
And what is the problem? Why don’t you just click the icon?
There were a built in themes but now it is gone
if I clicked the new theme it navigate me to a developing window
Correct. Only custom themes are still available. This has already been discussed in the forum. You can use the search funtion to find those discussions.