Why Do All My Photos Show the Download Date?
Every photo dated the day you downloaded them means the dates were never inside the files. Here is the fix.
Your computer gives every new file a created and modified date. When a photo has no date of its own, that is all any program has to show, so the whole export appears to have been taken on the day you downloaded it.
This is exactly what a Google Takeout export looks like. The real dates were not lost. Google put them in .json files next to the photos instead of inside them.
Takeout JSON Metadata Fixer reads those .json files and writes each real date back into its photo. After one run your library spreads back across the years. Free for your first 500 photos, then $9.99 once.