A 1080p label describes the picture dimensions, not every part of its quality. The source recording, compression and available bitrate still matter.
Start with the source
shortsdlyt.app lists formats that are available from the linked video. Upscaling cannot restore detail missing from the original, and changing a file extension does not improve its quality.
Balance size and playback
A smaller resolution can be convenient for a phone or a slow connection. Larger files can take longer to prepare and download. MP4 works on many common devices; WebM support depends on your player.
Temporary download links
Prepared files expire automatically to keep server storage available. Save the file while its link is active. If it has expired, prepare it again from the original video URL.