SharePoint Site 404 error on Home

Hi Sue12 , I am not sure if this applies to your case, but it’s possible that the page assigned as the SharePoint site homepage has been deleted. However, you should still be able to access specific areas of your site. For example, check these links:

Site content page:

https://<YourTenantName>.sharepoint.com/sites/<YourSiteName>/_layouts/15/viewlsts.aspx

SIte pages :

https://.sharepoint.com/sites//SitePages/Forms/ByAuthor.aspx

Default documents:

https://.sharepoint.com/sites//Shared%20Documents/Forms/AllItems.aspx 

 I hope that this was the issue in your case, and if so, you can set any page from the Site Pages as the homepage using this command ->