Can I still do it?

Yes! Back when Canvas updated to the New Gradebook, the "Mute" feature for graded assignments was replaced by the "Grade Posting Policy" feature. In order to hide (mute) assignment grades, you will need to set the "Grade Posting Policy" to "Manual". You can set the "Grade Posting Policy" at the course level and the assignment level.

How do I do it?

Set the Course Grade Posting Policy to Manual

Use this option if you want grades hidden in your course by default.

Click "Grades" to open the Gradebook.
Click "Settings" icon (gear at top right).
Select "Grade Posting Policy" tab.
Check "Manually Post Grades".
Click the "Update" button.

For more information (and screenshots) check out the Canvas guide on selecting course grade posting policies.

Set the Assignment Grade Posting Policy to Manual

Use this option if you want to hide grades for specific assignments.

Click "Grades" to open the Gradebook
Hover on assignment column header and click the Options icon (3 vertical dots)
Select "Grade Posting Policy" from drop-down menu
Check "Manually" on the "Grade Posting Policy" tray.
Click the "Save" button.

For more information (and screenshots) check out the Canvas guide on selecting assignment grade posting policies.

Hide Existing Grades

When you set a Grade Posting Policy to Manual, the policy doesn't apply retroactively. Use this option to hide grades in assignments that were graded before you applied the manual grade posting policy.

Click "Grades" to open the Gradebook.
Hover on assignment column header and click the Options icon (3 vertical dots).
Select "Hide grades" from drop-down menu.
Click the "Hide" button on the "Hide Grades" tray.

For more information (and screenshots) check out the Canvas guide on hiding previously posted grades.