Tomshardware claims some noticeable performance differences between the i9 10900K and the i9 9900K (at default speeds). For instance, there is a 11fps performance boost in Dawn of War 3, and a 10fps improvement in Far Cry 5 and GTA5.
Tweaktown claims that there is a 15fps difference in Shadow of the Tomb Raider. PCPer also reports a 10fps performance improvement in Metro Exodus. Additionally, PCPer states that there is almost a 50fps boost in DOTA 2. Anandtech reports a 10fps performance boost in Strange Brigade under the Vulkan API. Moreover, Anandtech reports a 14fps improvement in F1 2018.