EUSS Family Permit. Right to work
If your application was successful and you have been granted entry clearance in the UK in the form of an EU Settlement Scheme Family Permit, you will have the right to work in the UK.
You will not need any other document certifying this right. Your employer would breach the law if they refuse to provide you with work because you only have an EUSS Family Permit (which has not expired) and you have not been granted pre-settled status yet.
You must apply for pre-settled status within 3 months of your arrival in the UK if you wish to remain in the UK after the expiry date of your EUSS Family Permit.
If you want to apply for an EUSS Family Permit and need specialist advice, feel free to contact me. Please note that I am an accredited immigration adviser, not an employee of the UK Visas and Immigration. I charge fees for the advice provided.