I am facing the exact same issue.

It looks like I can click on any "line" in the black screen and type (beginning from the start of that line), but there is no way to execute the command.

I did a powerwash of my pixelbook and the issue is still present after the reset.

same issue here!!

it also crashes the os at the end of installation when it tries to start the container

Also got the issue here, no matter how many times I reboot or powerwash the device, still not working.

Is it possible to downgrade to get this working again?

I found the bug ...

From the dev console (since the terminal is part of chrome)
I could see that it was hitting error:

Uncaught TypeError: Cannot read property 'spokenFeedback' of undefined
    at hterm.Terminal.terminal.onTerminalReady (crosh.js:73)
    at hterm.Terminal.<anonymous> (nassh_deps.concat.js:11810)
    at hterm.Terminal.<anonymous> (nassh_deps.concat.js:12231)
terminal.onTerminalReady @ crosh.js:73
(anonymous) @ nassh_deps.concat.js:11810
(anonymous) @ nassh_deps.concat.js:12231
setTimeout (async)
(anonymous) @ nassh_deps.concat.js:2312
safeCallbackApply @ extensions::uncaught_exception_handler:27
handleResponse @ extensions::sendRequest:67

The code near the breakpoint finds chrome.accessibilityFeatures
is undefined so when it tries to access spokenFeedback it breaks.

  terminal.onTerminalReady = function() {
    chrome.accessibilityFeatures.spokenFeedback.get({}, function(details) {
      terminal.setLiveOutputForAccessibility(details.value);
      runCrosh();
    });
  };

Searching for the crosh.js source code found a fix that
hasn't propagated to our chromebooks yet.  It includes a test
to see if chrome.accessibilityFeatures is defined before it
attempts to access the values.

https://chromium.googlesource.com/apps/libapps/+/master/nassh/js/crosh.js?autodive=0%2F#73

    if (chrome.accessibilityFeatures) {
      chrome.accessibilityFeatures.spokenFeedback.get({}, function(details) {
        terminal.setLiveOutputForAccessibility(details.value);
        runCrosh();
      });
    } else {
      runCrosh();
    }

I confirmed this fixes the problem by adding a breakpoint,
pasting in the code, and resuming the debugger.

The fix is in this patch by Raymes Khoury <raymes@chromium.org>

https://chromium.googlesource.com/apps/libapps/+/3e44bc9eb923050b154ba64a813fe876646aef13

ping'ed Raymes Khoury <raymes@chromium.org> via email.

This is fixed on ToT and should be fixed in the next dev release (which hopefully should be in the next week or so). You should be able to work around it be installing the Chrome secure shell app from the web store.