How do I sort a collection of entries from multiple sections by date?
Rather than fetching the entries at first, just grab their IDs using ids() instead of find():

{% set featuredBlogId = craft.entries.section('blogs').limit(1).ids() %}
{% set featuredArticleId = craft.entries.section('articles').limit(1).ids() %}
{% set featuredSpecialReportId = craft.entries.section('specialReports').limit(1).ids() %}
{% set featuredInfographicId = craft.entries.section('infographics').limit(1).ids() %}


Then merge all of those arrays together:

{% set featuredIds = featuredBlogId
    |merge(featuredArticleId)
    |merge(featuredSpecialReportId)
    |merge(featuredInfographicId) %}


Once you’ve got that array of all the latest featured entries’ IDs, you can fetch their full entry models all at once:

{% set featuredEntries = craft.entries.id(featuredIds) %}

{% for entry in featuredEntries %}
    {{ entry.title }}&lt;br&gt;
{% endfor %}