SSI is not working

I’m trying to use server-side includes in a static site. But they don’t work.
Example: I created an index.shtml file and a text.txt file (in the root of the site)
Contents of index.shtml:

<html>
<head>
<title>SSI Test</title>
</head>
<body>
<!--#include virtual=”/text.txt”-->
</body>
</html>

Contents of text.txt:
<p>Text of text.txt</p>

The comment is not processed by the server in any way.

How can I make it work?

Conventional/classic web hosts run the web server for you. The web server they manage has configuration to run Perl against a .shtml file or anything in cgi-bin.

Render is not a web host, we are an application host, a platform host. We provide a compute instance (container), and you have to set up the web server, the interpreter, the configuration of both, etc. in order to accomplish SSI.
Static Sites don’t have an execution environment, but they have no underlying mechanism of running Server Side Includes either, they don’t have a “server side” in the context of execution.

If you don’t have the means to do so, you may want a more conventional webhost, such as something offering cPanel based hosting or something of that ilk.

Classic web hosts give you file space, Render gives you the whole machine.