The round trip.
Here is the whole exchange. Enter @mkbhd and the tool returns the channel ID UCBJycsmduvYEL83R_U4JriQ, the channel name and handle, the uploads playlist UUBJycsmduvYEL83R_U4JriQ, the RSS feed https://www.youtube.com/feeds/videos.xml?channel_id=UCBJycsmduvYEL83R_U4JriQ, and each channel URL format, all with copy buttons. Note the shape of the ID: UC, then 22 characters, 24 in total. Every valid channel ID matches that pattern, which makes malformed ones easy to spot.
The RSS feed alone justifies the lookup for many people. Paste it into any feed reader and new uploads arrive automatically, with no API key and no YouTube account. It lists recent uploads only, not the full back catalogue.
When a lookup comes back empty, open the input in a normal browser tab first. Misspelled handles, terminated channels and playlist links all produce the same silence, and YouTube sometimes shows a consent or bot-check page instead of the channel, which hides the ID.