The install script answers questions by itself

[kid-with-phone]

[WARNING] Missing dependencies -- the following commands are required for opam to
          operate:
  - bwrap: Sandboxing tool bwrap was not found. You should install 'bubblewrap'. See
    https://opam.ocaml.org/doc/FAQ.html#Why-does-opam-require-bwrap.
[ERROR] Sandboxing is not working on your platform android:
        /data/data/com.termux/files/usr/bin/opam: "create_process" failed on
        /data/data/com.termux/files/home/.opam/opam-init/hooks/sandbox.sh: No such file
        or directory
Do you want to disable it?  Note that this will result in less secure package builds,
so please ensure that you have some other isolation mechanisms in place (such as
running within a container or virtual machine). [y/n] n

Do you want opam to configure bash?
> 1. Yes, update ~/.bash_profile
  2. Yes, but don't setup any hooks. You'll have to run eval
     $(opam env) whenever you change your current 'opam switch'
  3. Select a different shell
  4. Specify another config file to update instead
  5. No, I'll remember to run eval $(opam env) when I need opam

[1/2/3/4/5] 5

Here I did not type 'n' or or '5' press Enter, it typed the answer by itself and continued.
This happens for all questions after "Where should opam be installed", both in install.sh and opam init.

~ $ opam config report
# opam config report
# opam-version         2.2.0
# self-upgrade         no
# system               arch=arm64 os=linux os-distribution=android os-version=10
# solver               builtin-mccs+glpk
# install-criteria     -removed,-count[avoid-version,changed],-count[version-lag,request],-count[version-lag,changed],-count[missing-depexts,changed],-changed
# upgrade-criteria     -removed,-count[avoid-version,changed],-count[version-lag,solution],-count[missing-depexts,changed],-new
# jobs                 7
# current-switch       none set
~ $

[kit-ty-kate]

That's fairly strange. This kind of behaviour would mean that either stdin is closed or Unix.isatty Unix.stdin (from the OCaml standard library) somehow returns false. I'm not sure if there is a special way to detect if the input of a terminal is available with termux compared to a regular POSIX environment.
Looking around didn't really give me any hint that it would be different so i have no idea what's happening.

I'll try to ask around if there are other people using android/termux