no canary are found for libapp.so binaries

This shared object does not have a stack canary value added to the stack.
Stack canaries are used to detect and prevent exploits from overwriting return address.
Use the option -fstack-protector-all to enable stack canaries.

Dart doesn’t generate stack canaries because,
unlike C++, Dart doesn’t have stack-allocated arrays
(the primary source of stack smashing in C/C++).

When writing pure Dart (without using dart:ffi),
you already have much stronger isolation guarantees
than any C++ mitigation can provide,
simply because pure Dart code is a managed language
where things like buffer overruns don’t exist.

In principle, you can create vulnerable code when using Dart FFI,
but normal use of Dart FFI would not be prone to these issues either, 
assuming it’s used with C code that itself uses stack canary values
appropriately.