How Do I Free Up Google Photos Storage?
Export your library, verify the copy, then delete from Google. The export is only safe once the dates are fixed.
The honest way is to take your photos out and keep them yourself. Export with Takeout, check the copy opens and is complete, and only then delete from Google.
Verify properly before deleting anything. A Takeout export with no dates is hard to check, because you cannot tell at a glance whether a year is missing.
Fix the metadata first and the library becomes checkable: browse by year and see the gaps. Takeout JSON Metadata Fixer does that step. It runs on your own computer and is free for your first 500 photos.