There isn’t a way to disable the Administrator login in QuickBooks. The QuickBooks user roles are important to provide restricted access to your employees, in order to protect sensitive company information like bank balances and account numbers. You can refer to this link to read more about the QuickBooks user and restriction:
Resolution for 'Administrator login issue: 'How do I disable the Adminstrator login at startup?' available: Yes.
The Administrator login issue or error code is a known issue in Quickbooks Online (QBO) and/or Quickbooks. Support for this issue is available either by self-service or paid support options. Experts are available to resolve your Quickbooks issue to ensure minimal downtime and continue running your business. First try to resolve the Administrator login issue yourself by looking for a resolution described in the article. If it is a complex Administrator login issue or you are unable to solve the issue, you may contact us by clicking here or by using other Administrator login support options.
For more information about resolving issues related to Administrator login in Quickbooks/QBO or to get support for the issue 'How do I disable the Adminstrator login at startup?', click the link below: