DTTG 4.1.1 on macOS Sequoia.
I seem to remember that I could search the pre-installed manual by typing a term into the search field under the Help menu. This has stopped working here, and it doesn’t resume after restarting DT nor after a reboot.
Assuming that it’s DT 4.1.1, then it’s working as expected on Sequoia & Tahoe (just checked this). Maybe the system’s help system is once again out of date or corrupted, reinstalling the app might help.