This shouldn’t be necessary. If you have your original images in a path, configured in ATTACHMENT_DIR, Discourse will create an upload (essentially, a copy of the file) in path-to-your-install/discourse/public/uploads/default/. If you check the Uploads table it should look like this:
[1] pry(main)> Upload.last
Upload Load (1.5ms) SELECT "uploads".* FROM "uploads" ORDER BY "uploads"."id" DESC LIMIT 1
=> #<Upload:0x0000000109a460a0
id: 196,
user_id: 251468,
original_filename: "Screenshot 2023-11-17 at 11.52.39.png",
filesize: 25174,
width: 398,
height: 248,
url: "/uploads/default/original/1X/2e5f7a09ba3bcd3a3597285771c53c16f20b18dd.png",
created_at: Fri, 17 Nov 2023 19:12:47.455954000 UTC +00:00,
updated_at: Fri, 17 Nov 2023 19:12:47.484137000 UTC +00:00,
sha1: "2e5f7a09ba3bcd3a3597285771c53c16f20b18dd",
Correct, looks like the nodebb script doesn’t migrate private messages. You can check other scripts to see how private messages are imported, check the Vanilla one for example.
The avatars are probably not being uploaded correctly, probably for the same issue you mentioned above.
No need for a plugin. You probably need to rebake your posts. You can wait for sidekiq to do so automatically, or you can run a full rebake from the console:
rake posts:rebake
The nodebb script hasn’t been updated in a few years, so my guess is that some parts of it are outdated and need to be modified in order for it to work with your data. Hope this helps!