Hi @Idan Greenberg ,
This is by design. /RoleAssignments requires the $filter parameter. This is documented here: List unifiedRoleAssignments - Microsoft Graph beta | Microsoft Learn
If you would like to leave feedback to enhance the Graph querying, you can leave it in the feedback forum. https://feedback.azure.com/
If the information helped you, please Accept the answer. This will help us as well as others in the community who may be researching similar questions.