Samsung has published a video showing how 12 hours of gaming effects different TV technologies. Samsung compare's it's own Q-LED (quantum-dots enhanced LED LCD TV) with LG's OLED TVs (the 2017 OLEDB7).
The video shows that following the extensive gaming run, Samsung's TV shows no image retention, while some problems are clearly visible on LG's TV.
This is of course not a professional or objective test. Image retention issues has been reported by many users on LG's OLED TVs, although there were also reports that the problem can be cleared by letting the TV show some different content for a few hours.
On a personal note, my own OLED TV (LG's OLEDB6), used for almost a year now, has no visible image retention or burn-in issues.