How to force Steam UI doubling on linux

In 2018 Steam on linux got the ability to autodetect HiDPI screens and resize the UI accordingly. I would guess this kicks in on 4k resolutions. I’m guessing because I don’t have one. What I do have is a laptop with a 14″ 2560×1440 screen and failing eyesight. Alas, neither one triggers the UI resize. Here’s how to consistently force the UI resizing instead of relying on Steam’s autoconfiguration.

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