Why Is My Photo Library Out of Order on iPhone?
Photos you import land in the wrong place in the timeline. Here is the reason and the fix.
The Photos app sorts by the date inside each file, not by when you imported it. If that date is missing, iOS substitutes the import date, so everything you just added piles up on today instead of spreading across the years.
Photos from a Google Takeout export cause this reliably. The date lives in the .json file, which iOS ignores completely. It only reads what is inside the image.
Fix the photos before importing and the timeline is right the first time. Takeout JSON Metadata Fixer writes the real date into each file on your computer, then you import. There is no way to fix the order from inside the Photos app afterwards.