A larger thumbnail canvas gives you room to retain useful detail from original artwork. It does not make a low resolution source detailed again. If a face is already a soft patch or a title has jagged edges before resizing, exporting at 1920×1080 simply gives that problem more pixels. Find the layered design, camera image, or clean frame capture first.
This page selects our 1920×1080 landscape preset. It is a practical export option rather than YouTube's largest recommended size. YouTube's current thumbnail guidance describes larger recommendations and upload limits that depend on the device. Check those requirements if you are preparing a particularly large desktop upload.
The same design also needs to make sense when the viewer sees it much smaller. Detail that improves the full image is useful only if it supports the main idea. Fine background texture should not compete with the subject, and a long title embedded in the image may become unreadable in a crowded recommendation list.