Beware! Google Photos app will delete your photos from your devices even with Back up & Sync disabled

A few friends of mine keep complaining losing their precious photos with Google Photos.  I am using Google Photos almost 5 years, but I have never encountered such an issue.  I always use the Web version of Google Photos for photo management, not the app.  The Web version is accessible via a browser while the app version must be installed before use regardless of on a phone or a desktop. 

To understand the deletion issue, I've recently taken Google Photos on my test run.  How and when are photos on a phone being deleted by Google Photos?  Is there a safe way to manage deletions on Google Photos?  The tests were manually done (1) on an android phone and (2) via the browser accessible to both desktop and phone with a single account.  

My current version of Google Photos app for test is 5.87.0444573954.

What I found is that the culprits of losing photos during deletion is using Google Photos app.  Unlike the Web version, the app always ensure the synchronized (or uploaded) photos deleted from the device(s), despite the option of "Back up & sync" disabled.  The only way to remove photos from Google Photos without removing from the device(s) is to have the "Back up & sync" option disabled first and then use the Web version for deletion.

• Whenever you delete a photo from a device via Google Photos app, the photo associated with Google Photos will be removed at the same time if the photo was uploaded and added into Google Photos before.  In this case, the app will always delete it from the device and Google Photos, despite the option of "Back up & sync" disabled.  

• Google Photos app provides an option for you to delete a photo from the device without removing from Google Photos. 
  
  
  
  
  
  
  There is no option for the other way around even though "Back up & sync" option is disabled.  In other words, the synchronized photo must be deleted from both the device and Google Photos.  Before deletion, Google has already provided a warning message (such as Remove from Google account & synced devices?)
  
  
  
  
  

• The only way to remove a photos safely from Google Photos is using the Web version of Google Photos (via Web browser) along with the "Back up & sync" option off.

I am not sure if Google does this on purpose or if it is a bug.   From the deletion message, it may be done by design.  It could be the reason why this issue has existed for a long time. 

In addition, my impression of using Google Photos app is actually handing over full control to Google (i.e., the Google Photos app), and your photos with Google Photos become a main copy, not the ones in your device(s).  Thus, when you delete a photo from Google Photos, the app will ensure to remove them from your device(s) without providing you an option to keep them in your device(s).

If you would like to manipulate photos in Google Photos without affecting your copy in your device, disabled the "Back up & sync" of Google Photos app, and then use the browser to handle the photo deletion.

For me, photos with Google are primarily for sharing.  I do not want Google to manage them in my device(s).  Thus, I will always have "Back up & sync" disabled and continue to use the Web version.