Native android apps can talk to regular USB devices, if granted the necessary permissions. But it's exposed through a Java api (and Kotlin I suppose, these days), which is fine, but it means you need to write your client logic twice. If you target the web, you can do it once.

(Yes, you could try to bulid some common interface, libusb-style, but I think you'll have a bad time with minor behavioural differences, especially around permissions. libusb itself does ostensibly support Android but there are several caveats: https://github.com/libusb/libusb/wiki/Android#does-libusb-su... )

So you can't just use fastboot in termux, with https://github.com/nohajc/termux-adb, then?