How to get top AND left navigation in SPO?

Ted1234 

You are right, you can have the top navigation with communication site & left navigation with team sites.

Also, currently Microsoft is releasing a new feature - SharePoint app bar to targeted release tenants & soon it will be available for all standard tenants as well. Using SharePoint app bar you can have the global navigation at the left side of your SharePoint sites (which will be shown on all modern sites - communication & team).

So, to have both side navigation, I will suggest to create a communication site & leverage global navigation in SharePoint app bar. Hub sites in SharePoint also have top navigation above site logo & title.

Check below articles for more information about SharePoint app bar & global navigation in SharePoint online:

1. Introducing a SharePoint app bar that features global navigation 
2. Enable and Customize Global navigation in the SharePoint app bar 

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