Leave Google Photos without losing the library

Get the files out, confirm you have them, then stop new photos from going to Google. Do not delete anything until the copies exist.

1. Export first

Follow How to export your whole Google Photos library with Takeout. Download every zip in the email, not only the first. Keep the zip files. Do not extract a huge library onto a disk that is already full.

2. Check a few files

Open photos from different years, not only last month.
Confirm the picture opens and the date looks right.
Do not delete the extra files sitting next to the photos. Those can hold the date.

3. Keep one copy on a disk you control

Copy the export to an external drive, or leave the zips on the computer if it has the space. This is copy one. The second copy is the next page. One disk is not a backup.

4. Turn backup off

Open the Google Photos app on the phone.
Go to your account photo settings and turn Backup off.
New shots stay on the phone. The old library in Google stays where it is.

Turning backup off does not delete what is already uploaded.

5. Do not empty Google yet

Wait until both copies are checked before you delete anything in Google Photos.
Shared albums and partner sharing do not come out as people. Tell anyone who shares with you before you leave.
A full storage bar is not a reason to delete first. Export first.

Next: Two copies of your photo library, without paying for two clouds.