Man pages matching name papi_unregister_thread in section 3:

PAPI_unregister_thread.3.en	debian 10 / libpapi-dev
PAPI_unregister_thread.3.en	debian 11 / libpapi-dev
PAPI_unregister_thread.3.en	debian 12 / libpapi-dev
PAPI_unregister_thread.3.en	debian 13 / libpapi-dev