Following the installation instructions for termux fails on multiple phones (including my own) with "Bad system call" when it comes to running git-annex.
My guess as to what has happened is that the arm64 build has been updated to use a newer version of glibc etc, and that is trying to use a syscall that the Android kernel is too old to support. (Kernel 4.19 in my phone's case.)
Unsure when it broke, but the arm64 build is built on Debian testing for whatever reason, so it's will need a reasonably recent kernel. Perhaps there should be an equivilant of the i386-ancient build for older arm64 systems? arm64 has by now been around as long as the Debian jessie used for i386-ancient. --Joey