On my non-rooted phone first I did
adb backup -all -apk -obb -f lenovo.ab and bit later
adb restore lenovo.ab (both commands had no errors). Surprisingly I did not find quite a lot of apps after the restore. There are two options: these apps were not stored in the backup file in the first command or they were not restored in the second. To check the first option, I made a tar file from backup with
dd if=lenovo.ab bs=24 skip=1 | openssl zlib -d > lenovo.tar (advice taken from Is there a way to look inside and modify an adb backup created file?) and did not find the missing apps there. So
adb did not store them.
The question is why? Probably many of the missing apps (or even all of them) were not updated for a long time. Can this be the reason to discard the app from backup?