Since Typo3 Version 9 you don’t longer need an extention to rewrite urls. All you need is a site configuration. The basic setup can be done with the UI. But at least for me an important setting isn’t set as default. The routes are servered withouth the .html extention.
How ever it’s very easy to extend this setting via a the config.yaml file. You’ll find this file at typo3conf/site/<name>. Just append these settings and you are fine:
... routeEnhancers: PageTypeSuffix: type: PageType default: '.html' index: 'index' map: '.html': 0