I have uninstalled all versions of LO from the other laptop, both the 5.x and the 6.0 developer. I installed 6.0 beta 2 and the .OXT file I had on the desktop no longer shows the extension icon since Windows/LO6 no longer sees it associated. Double-clicking in the .OXT opens a window asking which application to use to open the file. In simple words: if I only have one LO installed, it should associate the files, I believe, so it is a bug.
Update: Is seems all file associations were lost. MS Word 2016 opens all .ODT files and if we right-click on the documents and select to "Open With", LO 6.0 doesn't appear in the list of valid programs. In simple words, it is just like LO 6.0 beta 2 wasn't installed in Windows.
If I'm not wrong, because it's a beta version. In fact it doesn't replace previous version. Only RC versions are installed as released versions.