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I have no POS printer to test. If you couldn’t find a way you want in the official sample, it may be not supported to silently print data by a POS printer in UWP.
As you said, you have an approach to do this in WPF project. You could try another technology Desktop Bridge which you could use to add a desktop extension component(such as a WPF project) to your UWP app paakage. About the introduce of Desktop Bridge technology, you could refer to the document. About the detailed steps of Desktop Bridge technology, you could refer to the official document or a blog named UWP with Desktop Extension – Part 1 of Stefan Wick.
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