On Windows and Linux Thorium is the only reader to support most of FXL epubs generated by InDesign, but links between pages (such as buttons linking to another page) will not work. Otherwise everything works.
Reason for this: InDesign uses a non-standard javascript to link to pages instead of a standard anchor tag. It means that this must be fixed in code by manually unzipping the epub (epub format is a zipped file), and fixing those changes in a code editor.
PubCoder works fine, though, when creating an FXL epub with page links and viewing the result in Thorium.
But still the problem remains that users are required to install Thorium in the first place - something many users may not want to do just to read your fixed layout epub. This proves to be an additional hurdle: Mac and iOS read those FXL epubs without issues and users are not required to install yet another third-party tool.
Android: let's not go there. Not worth the frustration. Let's just say that FXL epubs are not supported.
To reach all platforms, an alternative is to use InDesign's online publishing option to publish your FXL book online, and share the link with your readers. This works in the browser, and anyone with a modern browser will be able to open it and view it. The drawbacks: dependent on Adobe's servers, will not work off-line, and it cannot be easily (if at all) monetized.
Another option is to convert your FXL ebook to an actual app, or to a progressive web app. The In5 plugin for InDesign supports these. A progressive web app only needs to be downloaded once, bypasses the app markets (you can share a link with your readers), and once downloaded can be read offline.
Or convert to an app which is basically an executable that can be run directly on iOS or Android - or even Windows, Mac, or Linux. Which means 5 different executables must be built.