Downloading all images from a Slack channel isn't a native one-click feature, but you can achieve it through administrative exports, third-party software, or custom scripts. Method 1: The Administrative Workspace Export
If you have permissions, you can use Slack’s built-in export tool. This creates a bulk archive of all public channel data, including file links. download all images from slack channel
Download all images from a thread post at one time? : r/Slack Downloading all images from a Slack channel isn't