Hello
Sorry I don’t have experience with backup since I never needed them. I use only a few applications: I migrate Signal to the new phone and copy the data + save contact and SMS on a computer and then to the new phone if I change phones.
I noticed that you use a S9+ with /e/ OS T and apparently have no problem. Can you please confirm this? I’m interested also if both back cameras work with /e/ OS T. Please answer me either here or preferably on my thread for this: Samsung Galaxy S9+ status with Android T