How Do I Fix Dates on Photos I Downloaded?
Downloaded photos usually carry the download date, not the real one. Here is how to correct a whole folder.
When you download a photo, your computer stamps it with the moment it arrived. If the photo has no date inside it, that download stamp is the only date anything can show, so the picture appears to be from today.
Sometimes the real date is still inside the file and only the file system date is wrong. Checking is quick: look at Date Taken rather than Date Modified. If Date Taken has a sensible value, the photo is fine and only the sorting is confusing you.
When the photo genuinely has no date, one has to be set. Takeout JSON Metadata Fixer can stamp a whole folder with a date you choose, or pull the right date from Google Takeout .json files if that is where the photos came from.