Your btrfs was in a LUKS partition and you can decode it? But know that btrfs uses smart compression by default, so you can recover jpeg or zip easily in general, but for stuff compressed, not sure how to decompress them by hand … Like other commenter wrote, first do a full copy on another HD.
I’m using video download helper, an extension for firefox https://www.downloadhelper.net/ and it can download about every video from web site. At one time it was not able so it asked me to install a Companion App and with it was able to dl from anime site and all.