Open YouTube
Go to the channel you want to block
Select the channel name or avatar to open the channel page
Click the channel’s “About” tab (if available)
Click “Block user” (or “Block”)
Confirm by clicking “Block” (or “Submit”)
On a video from that channel:
Open the video
Click the channel name next to the video title
Choose “Block user”
Confirm
On mobile (YouTube app):
Open the channel page
Tap the “More” (three dots) menu
Tap “Block user”
Confirm
To unblock later:
Open YouTube
Go to Settings
Find “Blocked users”
Select the blocked channel
Choose “Unblock”