World thumbnails are incredibly difficult to get right, and the worst part is that they are incredibly inconsistent. The most egregious issue is when a thumbnail is cropped into a portal; world creators shouldn't have to put up with their 4:3 thumbnails designed for the menus being cropped to the equivalent of a vertical phone aspect ratio. Image is attached for reference (credit to Maebbie) on how many aspect ratios you should expect to see during a normal session of VRChat today.

My proposition is incredibly simple: provide world creators with a new thumbnail dedicated to portals. Make it an optional feature (along with a fallback to the menu thumbnail if nothing is provided). Give creators the tools to make more immersive portal-specific designs to their worlds. It feels strange that portals can be customizable now, but creators don't get any say in how the inside of those portals will look once placed. There's a lack of polish to the way that the aspect ratio of the world thumbnail changes constantly, but it's especially jarring on portals themselves when it feels like there should've been a solution to this years before the customizable portals were introduced.