nginx sets proxy_set_header Host cannot access the proxy address

Recording a question, I don’t understand what’s going on. If anyone knows about it, please let me know.

 After setting this request, localhost:prot cannot jump to this address, but if you remove it, you can access it normally.

Parameter introduction: Introduction to proxy_set_header in nginx_nginx proxy_set_header_zdhxmm's blog-CSDN blog