Normal Purchase Users should only be able to see supplier invoices

The problem is that if you are also a sales user you can view customer invoices

All accounting users can see all types of journal.  

• What do you want sales, purchase and accounting users / managers to be able to see?
• Do you need purchase users to have access to sales orders and sales invoices?

It should be possible to create separate A/R and A/P access, but this needs to be done with care!

More information

Create Record Rules

• Go to Settings > Technical > Security > Record Rules.
• Define the following rules:

Rule for Normal User:

• Name: Restrict to Customer Invoices
• Model: account.move
• Apply for group: Normal User
• Domain: [('move_type', 'in', ['out_invoice', 'out_refund'])]
  (This filters customer invoices and refunds.)

Rule for Manager:

• Name: Access All Invoices
• Model: account.move
• Apply for group: Manager
• Domain: [(1, '=', 1)]
  (This allows unrestricted access to all invoices.)