One thing's for sure APFS handles all extended file system attributes very well - just plays better than HFS+. It may account for all the sandbodx mdwrite extended attribute problems (check a console log under HFS+) that ultimately affect how the software (like system update) accesses key assets like plists.you are very welcome very happy you asked for my install log after DP4 as you can see in the screenshots both my hdd's are APFS my internal MacIntosh hdd I formatted APFS when DP2 came out so maybe that's why I was able to successfully update since
Edit: thank god @dosdude1 has a neat and seamless APFS ROM patcher to handle the details. Thanks again.