It seems I accidentally deleted a whole (important) layer from a map I created on umap (and still use with public editability). Is there any chance to retrieve the data or possibly restore the layer completely?
I know it’s entirely my own fault and that I should have made a backup, but maybe there is still a chance?
You need to ask the operator of the umap instance in question if they have a backup (and are willing to see if they can help you). There’s nothing anybody here can do.