After installing LibreOfficePortable in the very same location, "C:\Program Files (x86)\Portables", where OOoP320 is still installed and running (so there is no "long paths" problem) together with many other portable applications, I found out it refused to start because of the spaces in the path.
I momentarily bypassed the obstacle buy moving the LOPortable folder in C:\, but this is not a place where I like to put applications.
I hope some solution or a fix will soon be suggested or provided, because the "remedy" I found elsewhere in the forum (renaming "Program Files (86)" to "Program_Files_(86)") can not, obviously, be any useful in a system where many applications, both portable and non-portable, are already installed.