Windows 11 24H2 26100.4652, Start11 2.53. 
I've always used LaunchBar Commander to have a toolbar of buttons on the right (image 1). 
After updating Start11 to version 2.53, the Launchbar expands to the entire right side (image 2). 
 
                       
                      
I uninstalled Start11 and reinstalled it: the problem occurs when I enable "Let Start11 improve the taskbar" in the App Bar. 
Now I leave the option disabled, but before the latest update, I used this option and the rounded edges of the taskbar, and LaunchBar worked fine.