Craft 3.6 Upgrade errors - can only install one of yiisoft/yii2 (and other errors) I'm new to Craft so maybe I'm doing something dumb, but I can't get past this error screen when trying to update to 3.6:
Composer output: Loading composer repositories with package information
Updating dependencies
Your requirements could not be resolved to an installable set of packages.

Problem 1
- Can only install one of: yiisoft/yii2[2.0.38, 2.0.40].
- Can only install one of: yiisoft/yii2[2.0.40, 2.0.38].
- craftcms/cms 3.6.5.1 requires yiisoft/yii2 ~2.0.40.0 -&gt; satisfiable by yiisoft/yii2[2.0.40].
- Installation request for craftcms/cms 3.6.5.1 -&gt; satisfiable by craftcms/cms[3.6.5.1].
- Installation request for yiisoft/yii2 (installed at 2.0.38) -&gt; satisfiable by yiisoft/yii2[2.0.38].

Running update with --no-dev does not mean require-dev is ignored, it just means the packages will not be installed. If dev requirements are blocking the update you have to resolve those problems.

I deleted the composer.lock file based on some threads I found here, and I tried running composer update from the terminal and it did reduce a much longer error message down to this one, but still no joy.
I'm developing locally on MAMP, 3.5.x was running great.
My composer.json:
{
  &quot;require&quot;: {
    &quot;craftcms/cms&quot;: &quot;3.5.18&quot;,
    &quot;craftcms/contact-form&quot;: &quot;2.2.7&quot;,
    &quot;craftcms/feed-me&quot;: &quot;4.3.4&quot;,
    &quot;craftcms/mailgun&quot;: &quot;1.4.3&quot;,
    &quot;craftcms/redactor&quot;: &quot;2.8.5&quot;,
    &quot;vlucas/phpdotenv&quot;: &quot;^3.4.0&quot;
  },
  &quot;require-dev&quot;: {
    &quot;yiisoft/yii2-shell&quot;: &quot;^2.0.3&quot;
  },
  &quot;autoload&quot;: {
    &quot;psr-4&quot;: {
      &quot;modules\\&quot;: &quot;modules/&quot;
    }
  },
  &quot;config&quot;: {
    &quot;sort-packages&quot;: true,
    &quot;optimize-autoloader&quot;: true,
    &quot;platform&quot;: {
      &quot;php&quot;: &quot;7.2.5&quot;
    }
  },
  &quot;scripts&quot;: {
    &quot;post-root-package-install&quot;: [
      &quot;@php -r \&quot;file_exists('.env') || copy('.env.example', '.env');\&quot;&quot;
    ]
  }
}
I found the fix here
composer install --ignore-platform-reqs