We have a special test build to check for performance issues by collecting telemetry data. With that data, we can see exactly where and when the game's performance issues happened.
Switch to the “perf_test” branch from the Steam Betas tab (Manage>Preferences>Betas). You can also use the "perf_test_beta" for the most current beta build related issues.
Open the game as usual and proceed to the stage where you are experiencing performance issues.
Before the performance issues start, toggle the profiling tool by holding the “right shift” and pressing the “T” key.
Record for 20-30 seconds, press the toggle key combination again. Please keep in mind that the more you record, the more upload time it will require.
Find the "test.tmcap" file in the "...\Mount & Blade II Bannerlord\bin\Win64_Shipping_Client" folder. You can find the "Mount & Blade II Bannerlord" folder inside Steam’s application library folder.
Finally, you can send the file to us via our ticketing system. If the file is bigger than 100 MB, you can use any other file upload site and send us the download link in your bug report thread. You can find more info about how to upload files to us with the new ticketing system here[forums.taleworlds.com].
It is appreciated if you provide more information about your PC, what you were doing while the game was recording and your graphics configuration.