I think the back gesture today is quite common, I find it very consistent and reliable. For a really good usability/accessibility (think about people with impaired hands movements) maybe on the first pwa run the app could ask if always on back/forward buttons are preferred, and show them on the bottom.

PWA apps don't have any other options that cannot be exploited on the standard browser view; some are pushed forward (ex. notifications) because are expected in a standalone app.

Don't worry about the bounty, was only a 5 minutes trivial update, I'm happy to gift some time to the project/community :)