Account settings import/export exists, but not a full data export. Part of the reason is that importing and overwriting historical data isn’t possible with activitypub.

But at least a full data export would be possible to do. Open up an issue for this in the lemmy back end.

No settings page (as far as I’m aware), but you can use the API to get everything (posts, comments, etc):

step 1: get login token -

curl --request POST \
     --url https://lemmy.ml/api/v3/user/login \
     --header 'accept: application/json' \
     --header 'content-type: application/json' \
     --data '
{
  "username_or_email": "2br02b",
  "password": "YOUR-PASSWORD"
}
'

step 2: use login token (big long string starting with ‘ey’) to get data -

curl --request GET \
     --url 'https://lemmy.ml/api/v3/user?username=2br02b&page=1' \
     --header 'accept: application/json' \
     --header 'authorization: Bearer YOUR-JWT'

Increment page number until you have everything. source: https://lemmy.readme.io/reference/get_user