I noticed that someone else had this same issue so I wanted to add in on it myself. I bought the camera back in November 2025. I use it all the time but mainly to shoot family picutres and travel pictures, nothing extreme. This happened literally from one day to the next. I can see it on my timeline of imports, clear frame one day and the next all pictures have this vignetting.
Apparently it's a light shield that comes lose on its own. I can actually see it when the camera is off and the sensor moves. It's clearly covering a portion of the sensor. It's most noticeable on 50mm and up. My 24mm lens doesn't show it as much as you can see from the pictures.
Anyway, I'm sending it in to Panasonic for repair and I'm hoping that this is covered under warranty since it's well under a year. A little disappointed with this build quality defect but at least I'm glad it's happening early on rather than later when out of warranty. I'll be extremely disappointed if they want to charge me a ton of money for this repair. I'll update as it goes on.