If you want to make 3DS games posts and own a Wii U, take screenshots with Rosalina Menu on 3DS, then move the screenshots to the Wii U's SD card, access them via Wii U Shell, and after loading the screenshot, press the Home Button to launch Miiverse and post your 3DS screenshot!
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you lost me at switching sd cards. Allat' just to post a photo of a 3ds game? there's gotta be a better way.
And if you wonder... Open Rosalina Menu : L+↓+SELECT Screenshots path : SD/luma/screenshots/
EGbossss, all that to post multiple 3DS screenshots! Once it's done, it's fast! An alternative way is to stream your 3DS to your Wii U, but it's less convenient imo.
The original Miiverse had 3DS posts implemented, Pretendo will update Juxt in the future with that feature restored eventually. That's the best work around for now.