SharePoint's modern web experience comes with a default Communications Site which is great as long as you want to use it. For us, we already had an existing Teams-style site that we wanted to be users' homepage when they browsed to SharePoint.
SharePoint Admin will show you a button (upon selecting the Communications Site) called Replace Site. Unfortunately, the new site must follow strict requirements including having no groups in Microsoft 365. In fact, you'll receive this message when attempting this:
This site must be a team site or communication site. It can't be connected to a Microsoft 365 group.
There's a "hacky" way to get around this though!
- Browse to the default, root-level, Communications Site in SharePoint.
- On the homepage, click New and then select News Link.
- When prompted, set the link to the URL of the SharePoint site that you want to be the homepage (ex. https://company-admin.sharepoint.com/sites/SiteName).
- Post the News Link.
- Browse to the site's Pages by clicking Pages on the top navbar.
- Right click on the News Link that you just created and select Make Hompage.
Now, when you browse to SharePoint's home (ex. https://company-admin.sharepoint.com), you'll be instantly redirected to the site you have chosen.