Man pages matching name ssl_ctx_sess_set_cache_size in section 3ssl:

SSL_CTX_sess_set_cache_size.3ssl.en	debian 10 / libssl-doc
SSL_CTX_sess_set_cache_size.3ssl.en	debian 11 / libssl-doc
SSL_CTX_sess_set_cache_size.3ssl.en	debian 12 / libssl-doc