As of 2024/03/23, the new Bold Animation Pack has inconsistent thumbnails compared to other animation packs.
For most other animation packs, including the Toy Animation Pack, the animation preview is displayed on a white blocky character with no clothing.
Expected behavior
For the issue with the clothing, either the new animation pack thumbnails could have the clothing removed, or a different bundle could be used to be more in line with how Emote thumbnails work.
The main issue was how at the time of bug report creation the thumbnails were inconsistent across various bundles, but it looks like they’ve all been regenerated by now and that inconsistency is gone.