The [assembly: obfuscation] does not react to the parameter PublicMembers := true.
And in the documentation is stated:
This metadata is stored in the .fx file, so that the binary files (such as .dlls, .jars, or .a files) that will eventually be distributed to your end-users only contain the obfuscated names. When targeting .NET or Java (which does not emit .fx files by default), you will want to enable the Create .fx File option in project settings, to enable this.
I can not find this setting anywhere.