Hello @Fair_Trader ,
You can add non-openers to lists via the sent email's report. Simply go to the specific email's drilldown for its Did Not Open rate, then click the top-most checkmark box to select-all, then Actions > Add to List, and either create a new list or add them to an existing one.
For step-by-step and visual guidance, make sure to check out this article regarding emails' Did Not Open report.
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