I have 992GB of photos stored in Google Photos and I desperately want something to transfer all of them FROM Google Photos to any other service.

Google Takeout fails to export all of my photos..

I have 400GB in Google Photos, and I am able to use Google Takeout to download them as multiple archives. I try to back them every 1/2 years on a hard drive.

Since I assume you are a Google One user. Maybe contact support and share your issue?

Does it actually miss data that should be there or does the Takeout fail?

Did you try rclone ?

Rclone can't download original quality files from google photos(API limitation)

Thanks, I had no idea.