You can do that on Opera as well!
Go on Settings and under Search Engines press "Add", then you need to complete the fields. Do that this way:
- Search Engine: Custom Description;
- Key: the word you want to use for this search engine. In your case it would be "y" but I think you can't use 1 single character on Opera, I used "yt" and it worked for me;
- URL: this is the URL the browser has to use to start the query. For YouTube it would be "https://www.youtube.com/results?search_query=%s". The "%s" in the URL will be replaced with the text you search.
Now save it and it should work! You just need to use write <key> <what you want to search for> on the address bar and it will search directly in YouTube! Please note that you just need to put a space between the key and the text. You can do that with a lot of websites, personally I use it for Wordreference (dictionary).
I'm on Opera GX but it should be similar (if not the same) for Opera.