I used Canva Magic Media to try making a YouTube banner for my channel. Signing in and searching "youtube banner" both worked fine. I got shown a template, already sized at 2560 x 1440, but stopped there before going any further with customizing it, adding text, or downloading. So I never got to the part where it checks the file size or guides you through uploading it in YouTube Studio. I didn't end up with a finished banner to check. Based on what did work, it seemed promising. I ran out of time today; the template search alone saved me hunting for the right size.