I am using a rooted Samsung S8+. But, Termux cannot gain root access. I tried
When I tried installing termux-sudo, I had the error
cat: sudo: no such a file or directory.
(Tap to enlarge)
First, you probably need to use su rather than sudo. Where did you copy the sudo from? It looks like some incompatible executable, maybe copied from an x64 distro (guessing).
Second, Termux overrides $PATH. You will need to provide full path or to make su available on $PATH. You might want a symlink (ln -s) of su (which might be located in /sbin/, /system/xbin or so).