Dear Aimee,
Sorry for the delayed reply.
I do a test with the permission level you showed in the screenshots above and users should see all items in the specific list.
I'd like to confirm whether the users can only see the newly added items created by them in the specific list each time when they add the new items each time.
If yes, I guess that someone in your company creates a flow by using Power Automate to restrict users' view in the specific list. For example, the flow can be created as follows.
Condition: When a new item created or modified by a user.
Result: Remove the user permissions on all existing items in the specific list and only grant user permission on the newly created item added by the user.
If
the user add item 8 on the list, the flow will be automatically ran and the user's view will become the following on the list.
The site owner view is the following on the list.
So I suggest you contact other users and go to Power Automate to check whether someone creates such a flow created on the affected list in the site. If yes, let the flow creator removes the flow to see the result.
Best Regards,
Cliff