I wish on Lemmy you can just go to you're camera role and just click on or press on whatever photo you need for your post

I copied this to clipboard from my phone's photo album then pasted it directly into my post. Sh.itjust.works runs an image server that allows this and I'm guessing other lemmy instances do as well.

I copied this from image search results on duckduckgo and pasted it right in.

I do not know of a gallery view like you described where you can swipe left and right to view the images.