In Locker Service (LS), they use an ObservableMembrane with a readOnlyMembrane within it that protects cached values. This membrane immediately rejects any writes to the protected object. If you attempt to write to an existing property, you get an error that reads Cannot assign to read only property 'x' on object, while if you attempt to write a non-existent ...
Fields and objects each have their own security. You are expected to check every object and field, e.g. MyCustomObject__c.field1__c.getDescribe().isCreateable(). You can simplify these checks with Security.stripInaccessible.
Based on docs Account team access is only visible if the user having below access,
Edit access on account record.
User is an Account owner or User need to available in above/parent Role of the Account owner's role in Role hierarchy.
Please let me know if it helps.