The Blackboard Grade Center functions differently than Canvas Grades. Canvas Grades columns are all connected to some type of assessment. In Canvas, you modify columns in Grades by modifying or creating new assessments. Assessments can include Assignments (of all types, with or without a submission), Quizzes/Surveys, and graded Discussions.
Blackboard columns do transfer to Canvas but you will need to review and modify them as necessary.
Manually created columns import as an Assignment with Type set as no submission. Blackboard Grade Center categories will import as Assignment Groups.
For more info
- Grades in Canvas https://community.canvaslms.com/docs/DOC-4131#jive_content_id_Grades