Okay, now I get it. So apparently, I should upload photos on videos from the third tab of amethyst to make them show up in the gallery section of my profile. Thanks. Out of curiosity though, any particular reason why regular uploads of photos and videos don't show up in gallery? Why does it treat them differently?

If you upload them on Notes, then they stay inside the notes and can be seen from threads and replies as usual. The gallery only shows the posts made for images and videos directly (not notes)

Da para publicar fotos na terceira guia usando smartphone?

Yes. Go to the third tab of amethyst from your smartphone. Then tap on the new photo/video icon and choose whether you want to upload photo or video. After that, select the photo or video you want to upload and voila.