Read/Write permissions in a SharePoint List

Hi Angus_Ball - for users to only see their own items, this is a List Setting; see this article: How to enable Item Level Permissions in SharePoint | SharePoint Maven.

For users to not be able to edit a column, you have two options:

1. Only allow editing via the Power App, not the List so you can set permissions via the app. See Set up security permissions for a column - Power Platform | Microsoft Learn. And you'll want to suppress the List from search results so they can't still find it to edit. This is an old article but still accurate Exclude SharePoint Site or List from Search Results - SharePoint Diary

2. Replace the current column with a Lookup Column in a new List and set the appropriate permissions on that List. Regardless of accessing via List or Power App, only those with permissions to the Lookup List can use the column.

Both options require updates to the App. I hope that helps!