Replacing google slides images using slides api in shared google drives

Question

Following up with my previous question, now, facing an error when I use shared google drive with the service account having Manager privilege on that shared drive, it is failing during the image replacement in google slides. In addition, using my personal account I can edit any file on that shared drive, with that I have two questions:

1. why slides API's batchUpdate method needs public access when used to replace images in slides using replaceImage ?

2. what is the difference when interacting with the shared drives with personal account and service account ?

Any suggestion and help appreciated, note: I am still learning about google API's. Thank you in advance.

used personal account to edit the slides it works.