https://bakapervert.wordpress.com/arifureta-chapter-401/ I believe this was the latest one. Also, I think bakapervert translates these as they come out, so its entirely possible there are more and that the author just hasnt written them yet. He seems to like to bounce around a bit when writing these after stories after all.
It does not really seem to be truly over. The series pops in and out of it. Bakapervert’s site has the table of contents of the afterstory with arcs listed based on titles. You can also check the wikia fandom site for more in-depth explanation of the cosmos in the Arifureta-verse and the inventions/items he has crafted