About API Web Serial ....
It's not work on android brousers
but webusb - work
https://selevo.github.io/WebUsbSerialTerminal/
support ch340 pl 2303 ft232 and others
it's projet other autor but i consilidate in one page.
In code more bugs but work
This allows you to use a smartphone as a display, mathematical apparatus and visualization tool for any devices that require a display, and the user can save on this and in DIY
Developers will use this option for connecting control and display. besides, many people have at least two smartphones lying around in their drawer 
and + use about://usb-internals
also Use USB debugging It also works in the mobile version of the Chrome browser
