Weird .download files keep emerging in Downloads folder
Apparently, Telegram Desktop generates these files during "failed" searches when using the @gif command. The ones that Telegram generates are easily identified by being named with a series of 18 digits (e.g 532576936841446647.download), usually similar to one another, and always at zero-bytes length.

You can replicate the issue by trying some @gif searches after removing all files and seeing them being generated again.

They're safe to be removed; watch out not to remove the Safari ones, though, unless you'd like to restart your ongoing downloads.