Dynamic linking is indeed specifically exempted with the LGPL, but static linking is not; building a statically-linked binary would require the whole program to be under the (L)GPL.

Exactly. And embedding in an app or firmware that needs to be signed before deployment, in other words, the end user cannot update the lpgl part and deploy this new binary on the device, is seen as static linking. Since lgpl 3 even the legal gray area of Tivonisation is taken care of.

Which might some people wonder if the use of flow9 in a closed source Android or iOS app is even allowed. Can the end users create a new version of the app with an updated version of the lpgl3 lib AND deploy this library on their device? Normally they can not, but you can provide your binaries and build scripts to be compliant. See also this answer (not by me): https://stackoverflow.com/a/39438539

So in the end only for closed source non user updateable (signed) firmware, the use of LGPL3 is impossible. Think about most TV settop boxes or payment terminals.