So all the steps above are correct the way they were described. The only thing I have done wrong was, that my target DLL was modified by Mono.Cecil before (I already had read and wrote my target DLL and modified it by this way). So the DLL and the PDB was not the same anymore.
So if you want to run Mono.Cecil just once and you get the exception above do the ...
Since Android 10.0, it has move some of its important library into different path ( including libc.so )
so IDA can't automatically found where it is like it used to.
You need to execute export IDA_LIBC_PATH=/apex/com.android.runtime/lib/bionic/libc.so to tell IDA where libc.so can be found.