Like others mentioned, request Google Takeout which gives you all your photos. I recommend keeping the original zip/tar.gz for future reference (e.g. you need specific metadata not included in the photos directly).

Also, make sure to keep backups. E.g. upload it preferably encrypted, and store the password in a password manager. Make a copy on a USB SSD, and not just the Steam Deck (you might wipe it, lose it, …).