Sorce where I found it online: https://duckduckgo.com/?q=lineage+os+standart+wallpapers&t=fpas&iax=images&ia=images&iai=https%3A%2F%2Fwww.setaswall.com%2Fwp-content%2Fuploads%2F2018%2F02%2FLineage-OS-15.1-Stock-Wallpaper-03-2560x1440.jpg
It's one of the preinstalled wallpapers on lineage os 17.1 I can try to post it in the comments.