Manual sharing is a way of granting access to individual records by manually sharing them with other users, roles, or groups. Manual sharing can override the organization-wide default and role hierarchy settings and give additional access to specific records. In this case, manual sharing could be the reason why only one user can see the account record, even though they have the same profile and role as another user who cannot see it. Reference: https://help.salesforce.com/s/articleView?id=sf.security_sharing_manual.htm&type=5