We have added this to our to-do list, the pop-up message will be available in wpForo 2.0 version.

would need to hide the password change field, to keep account management all out of the forum.

Password change cannot be disabled, but you can hide it with CSS code: Insert The CSS Code in Custom CSS Code field from Dashboard > Forums > Settings > Styles Tab

.wpf-field.wpf-field-type-password.wpf-field-name-user_pass.wpf-field-required {
    display: none;
}

Posted by: @alice79b

Instead now, if I ask for a change of password, as soon as I push the button, the logout is made and I am redirected to the login page.

If you press Save Changes button after you entered the new password, the Page will be refreshed and the new password will be set. There is no pop-up msg that says that the password has changed but about that I can ask our Devs, for a solution.

At this point, as user, I don't understand what happened, and I don't know if the new password has been taken until I try to use the old one or the other. As usability it is not optimal.

Maybe you meant to check here: https://wpforo.com/docs/root/addons/wpforo-user-custom-fields/field-settings/ ?

Oh, sorry I gave wrong Doc. Your mentioned doc is the right one.

Posted by: @alice79b

But if I really can't hide it, can I avoid to get logged out and redirected to the login page, without any message of confirmation?  

I don't follow you.

Check this Doc for more Info: https://wpforo.com/docs/root/addons/wpforo-topic-custom-fields/