OXPS documents can be created in Windows 8/10 as an export/or print via XPS virtual printer. Your best shot for oxps to html conversion is to first convert oxps to xps, which is a little more supported format. Once you have the .xps file, you need to use of the XPS conversion tools to try to export it as HTML files with which could work. Sometimes you would need to convert xps to pdf first before finally converting it to the format you need.
Open OXPS file Open HTML file