Can I create multiple accounts in the Sinch Build Dashboard?

No, currently it is not possible to create multiple accounts in the Sinch Build Dashboard. You can create another account using a different e-mail address, and invite your main email to that new account, then you will be able to switch between accounts from the account selector in your profile menu in the top bar:

Click the arrow next to your existing account and select the account you want to switch to, from the drop-down list.

Refer to the Sinch Account Model article to learn more about SInch Accounts and how to manage your resources for different requirements.