Why can't I get into the homepage of the company website without adding "index.php"? What happened? Ask the great god to solve the mystery, thank you!

IIS server needs to set the default page, otherwise it will default to index.html, and you can't access it, because there is no index.html in the root directory of your homepage. You can add multiple pages simply by adding index.php to the default settings, and IIS will display them in sequence.