Hi @Markus W & @Ercole G,
It's quite simple ;-)
The web app is developed as standalone (Xojo 2017v2.1) and runs on a small Win10 PC, listening a port.
Clients are Android tablets (Huawei T5).
Small LAN, no internet connection.
On each table I installed the kiosk app Fully Kiosk Browser (via google play).
In Fully Kiosk settings I specify my Win10 IP http://address:port as "start URL", and voilà ! The web page is displayed full screen, no annoying message about insecure url.
No status bar, no address bar, ...
Fully Kiosk is using Android Webview (Chromium) and seems to be fully compatible with the Xojo web apps.
For some tablets, placed in public areas, I bought the "Plus" license to make it impossible to quit the Web App without knowing a PIN code.
The Plus license is 5.90€ per device, taxes included, volume licenses available (> 10 devices).
I'm using Bluestacks (Win & Mac) Android emulator. It's free and it lets you install Fully Kiosk via google play to test all features (including "PLUS") before buying.
Bluestacks is really performant, installing Fully Kiosk is easy.
Using Bluestacks I could test all Fully Kiosk PLUS features without buying a license and without annoying message or watermark.
On the real devices, there are big watermarks if you use PLUS features without buying the license.
If you need more details tell me.