you mean for the Touch Bar?
Unfortunately that’s currently not possible as Apple changed how the side car Touch Bar works in the final Catalina versions - it is now some weird display and app-specific Touch Bar that only shows if apps are active on the side car display.
Would be great if everybody who wants BTT working on Side Car would file a bug/feature request with Apple which requests that Side Car should just mirror the main Touch Bar. No need to mention BTT. (it was working beautifully in the betas)