what is proper cross-posting etiquette

if you want to cross-post the same exact image to a different community there should be a link at the top of this post to cross-post (if using the desktop web ui), it sorta looks like a copy icon

but if you wanted to use a new photo then I think just creating a new post over there is probably easiest

I've gone ahead and subscribed to that other community, hopefully it gains some traction. I enjoy seeing old finds from yard sales, etc