To implement field-level security, a system administrator performs the following tasks.
Enable field security on one or more fields for a given entity.
Associate one more existing security profiles, or create one or more new security profiles to grant the appropriate access to specific users or teams.
A security profile determines the following:
Permissions to the secure fields
Users and Teams
A security profile can be configured to grant user or team members the following permissions at the field level:
Read. Read-only access to the field's data.
Create. Users or teams in this profile can add data to this field when creating a record.
Update. Users or teams in this profile can update the field's data after it has been created.
Reference:
https://docs.microsoft.com/en-us/power-platform/admin/field-level-security