Can you check the output of the following commands:

asdf which elixir
asdf which iex

~/.asdf/installs/elixir/1.11.2-otp-23/bin/elixir
~/.asdf/installs/elixir/1.11.2-otp-23/bin/iex

Did you try asdf reshim ?

Yes of course.

Using iex with full path works but using only iex command does not work ?

~/.asdf/shims/ folder is included in path.

Commands like iex, elixir, erl are resolved to files in the shims folder.

You can check $PATH variable if ~/.asdf/shims/ folder is included.

Did you install asdf using brew ?

Also not sure if it’s any help, but try following this guide - this has always worked for me on a new Mac or after a clean install.

I have

plugins=(
...
asdf
...

in .zshrc
and then

asdf reshim elixir

Try mix local.hex what that do for you

I would also try a dumb terminal with no zsh, see if that functions normally so you can narrow the surface area of this bug.

So if I type in these commands:

(base) ➜ ~ asdf which elixir
HOME/.asdf/installs/elixir/1.11.2/bin/elixir
(base) ➜ ~ HOME/.asdf/installs/elixir/1.11.2/bin/elixir --version
HOME/.asdf/installs/elixir/1.11.2/bin/elixir: line 230: exec: erl: not found

I get the error above.
So I tried fixing it with setting export erl=HOME/.asdf/installs/erlang/23.3.4/bin/erl
in ~/.zshenv

However
(base) ➜ ~ echo $erl
shows me
HOME/.asdf/installs/erlang/23.3.4/bin/erl

but just typing
(base) ➜ ~ erl
zsh: command not found: erl

Seems to me this is a zsh issue or I’m making a mistake?

Setting erl variable in environment is different from adding it to $PATH.

if you want to erl to path - it should be
export PATH=<path_to_exec_parent_folder>:$PATH

You should be adding ~/.asdf/shims if it is not present.
Can you try this:

export PATH=~/.asdf/shims:$PATH

And check iex, erl, elixir commands