For public accounts: Anyone on Instagram can download your reels and share your reels, unless you change your reels download settings. New reels you share after downloading became available will be able to be downloaded. For Instagram users under 18 with public accounts, the default setting for downloading reels will be off, but can be turned on at any time.
For private accounts: No one on Instagram can download your reels, unless you change your account's privacy setting to public.