You may wish to release to students the feedback separately from the grades on an assignment. This may be so that you can prompt students to engage more deeply with feedback, maybe to use the feedback on a second piece of work, or show students a a later date what their earlier draft would have been worth prior to acting upon feedback, or it might just be that an assignment is ungraded. We're normally a bit nervous around Canvas's 'Post Grades' settings (mainly that students might receive feedback or grades prematurely), but it has functionality that can accommodate varied feedback processes.

Here is a workflow that demonstrates a process for releasing feedback separately from grades:

Ensure 'Manual Post Grades' setting is applied in the course, to prevent feedback (and grades if being left) from being released automatically instructions here: Manual Post Grades. Then give feedback comments for submissions in SpeedGrader. (You can confirm the assignment is muted/hidden through a struck-eye symbol that will appear on the Grade column and in SpeedGrader once you leave your first comment or grade).
Use the Post Grades option to release the feedback - even though no grades were entered yet it will release any feedback left so far
At a later point add grades and students will receive them instantly as you leave them. OR if you'd prefer they all receive at the same time, you can reverse the Posting of Grades, give additional feedback/grades and then re-release.