Is there /etc/shadows in android termux? I tried the following:

$ pwd
/system/etc
$ ls | grep 'shadow'


But nothing was found.
No. There isn't

Keep in mind that Termux is only a Linux environment. It's at least vastly different from a real GNU/Linux system.

Android has its own Unix user system, which does not have logins and passwords. So you'd not expect /etc/passwd and /etc/shadows to exist.