You've chosen a 4K YouTube video to download, posted the link in SYC 2, selected the 2160p quality, but the grey box next to the video thumbnail still says "1440p" ?
If this is the case, please accept our sincerest apologies for the inconvenience. Our developers' team has been informed about the issue. We are going to release the fix in future updates.
Your understanding and patience are much appreciated!