To begin with, we assume you have your lovely home page ready in Modern Experience. If you haven't got it ready yet, we recommend you to do it first.

You can see Pages in your left navigation / quick launch menu as shown in below diagram

If by any chance you are on communication site or you made your quick launch disabled, you can go to Site Content -> Site Page Library

First step here is to ensure you keep your pages library in modern experience.

Select the page you want to promote as home page;

Click on more options (the three dots next to page name) and select Make homepage option

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