First, part of my confusion was that the installer effectively asks your OTP path but I think it used to actually install OTP? So I didn't read the dialog carefully and didn't realized it changed, my bad :)
But, after installing Elixir and pointing it to the otp 25.0.4 folder.
> elixir -v
> Cannot find file at 'c:\program files\erl-24.0\erts-12.0\bin\erl.exe' c:\program files\erl-24.0\erts-12.0\bin\erl.exe). This usually indicates a missing or moved file.
I install erl-24.0
> elixir -v
> Could not load module C:\Program Files\erl-24.2.2\erts-12.2.1\bin\erlexec.dll.
I install erl-24.2.2
> elixir -v
> {"init terminating in do_boot",{undef,[{elixir,start_cli,[],[]},{init,start_em,1,[{file,"init.erl"},{line,1191}]},{init,do_boot,3,[{file,"init.erl"},{line,889}]}]}} init terminating in do_boot ({undef,[{elixir,start_cli,[],[]},{init,start_em,1,[{_},{_}]},{init,do_boot,3,[{_},{_}]}]})
All the while erl-25.0.4 doesn't seem used (while being in the PATH env), I guess that's the problem but how do you enforce the OTP version?
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edit:
So I kinda made it work. First I noticed that I had erl-24.0 installed by Chocolatey (which I don't remember using ahah) so I uninstalled that.
To make it clear, I'm on Windows 7 so the problems may come from that, but maybe it will help somebody else.
But then the elixir-websetup.exe (2.2) would not actually complete any longer (while doing so when erl-24 was installed by Chocolatey?), it could not find the actual elixir downloaded installer in C:\<Me>\etc (not the valid user path in Windows 7 but maybe in 10+ ?)
I then used elixir-websetup.exe 2.1 and got almost the same error but this time it complained about "elixir-v1.14.1 (Erlang/OTP 25)-setup.exe" while it actually downloaded "elixir-v1.14.1-setup.exe", which I was able to launch myself and finish the setup.
I couldn't get Elixir 1.14 to work in September actually and reverted to 1.13.4, maybe I should try again.