How to make such a config?

Question

Nginx

If locationany other than /api/, then we return index.html, and if location = /api/then proxy_pass localhost:4200

Answer 1

location / {
    rewrite ^ /index.html break;
}

location = /api/ {
    proxy_pass http://localhost:4200;
}

Answer 2

location /api {
proxy_pass
}

location / {
что там вам нужно
}