You can also click on the bottom right corner of the cell that contains the value you want to copy down, and when it changes to a small square you can drag it down to the cell below (or to the cell(s) right,left, above. Also, for text, typing in an initial letter will often "fill" the string.
I had this problem recently and found this question so I will add an answer for others.
I turned out to be a Chrome extension that was overriding the Google Docs hotkey.
I went to chrome://extensions/shortcuts and looked for an entry with Ctrl + Shift + L and reassigned it to another key. You could also, of course, delete the entry if you do not use the ...
I've finally found an official post here with Youtube shortcuts, which also seems to work on Youtube Music.
Instead, there is an unofficial answer by an user with a complete list of shorcuts available in Youtube Music here.
The following shortcuts are reported from the unofficial post for Youtube Music.
Note: This list is unofficial, may not be complete ...
As of 2020, shortcuts do exist and the shortcut is g + n for the next page and g + p for the previous page.
But for any keyboard shortcuts to work, you need to have them enabled in settings though!
You can find a detailed list of shortcuts here in the google support page.