Newlines missing on Matrix for Slack formatted messages without blocks

[twouters]

The following message from Slack doesn't properly render newlines in Element. (Might be an issue with this client and not for other clients but I suppose compatibility is somewhat expected.)

{
  "type": "m.room.message",
  "sender": "@twouters:matrix.tcpdump.be",
  "content": {
    "body": "**bold** line 1_italic_ line 2line 3",
    "fi.mau.double_puppet_source": "mautrix-slack",
    "format": "org.matrix.custom.html",
    "formatted_body": "<b>bold</b> line 1\n<i>italic</i> line 2\nline 3",
    "msgtype": "m.text"
  },
  "origin_server_ts": 1681735582179,
  "unsigned": {
    "age": 133
  },
  "event_id": "$OYl0mLzdvF5YInrKJlhfm_T3qu-DxwcS_LsmYXXXXXX",
  "room_id": "!ftBtKtxVHpQhXXXXXX:matrix.tcpdump.be"
}

[tulir]

In my experience it was missing for Slack messages formatted with blocks, which is now fixed, but let me know if not (with the exact method to send the message on slack)