So it's only files in Downloads that have gone? If so that's an app has done it, not a hardware fault, because files in a folder are not actually stored in the same block of storage in the device.
The culprit could be a device care/storage cleaning app, either one you installed or one Samsung included (they no longer seem to include the CM-derived junk they added a few years ago, but since my s21's settings list apps I've used recently or even fairly frequently in their list of "unused apps" I don't have great faith in Samsung in this respect). Anything that might be used to free up storage. Conceivably even an accident with a file explorer could do this, though you'd need to accidentally select everything in the folder and then hit delete, which makes it less likely. Not knowing what apps you have installed or what system features this model has I can't really guess the culprit.
As for getting them back though, probably not going to happen I'm afraid. I don't know of any reliable file recovery for Android (there are apps that claim to do it, but finding reports of success that are independent of the software vendor is suspiciously difficult). And you can forget any solution that requires root, since even if you can root your phone (US model Samsungs usually can't be rooted, others usually can) the process will probably involve a factory reset, and a reset will destroy the encryption key and guarantee that the files cannot be recovered.