In VSCode, the default keyboard shortcut bindings to switch/toggle between the terminal and active editor is

ctrl+`

(ctrl+backtick)

The problem is, when switching back to the editor, it closes the terminal pane. If you want the terminal to remain open when switching back to the editor, you'll need to change the keyboard shortcut for at least the command workbench.action.focusActiveEditorGroup

Personally, I also don't really like moving my hand so far to press ctrl+backtick to switch-to/open the terminal, so I change that as well. The command for that is workbench.action.terminal.focus

Follow the steps below to change the keyboard shortcuts.

How to set the keyboard shortcuts

This superuser post suggests using ctrl+k, but this is a bad idea, because it will interfere with several existing two-part keybindings that rely on first pressing ctrl+k. Ironically, that conflicts with the keyboard shortcut that opens the Keyboard Shortcut UI itself, which is ctrl+k, ctrl+s. 😄

We'll use different bindings that haven't been used by default yet.

Open the Keyboard Shortcuts UI.
You can do this by pressing ctrl-k, ctrl-s, or using the menus: File -> Preferences -> Keyboard Shortcuts.

Copy and paste workbench.action.focusActiveEditorGroup into the search box.

Click the + button on the result, bind it to ctrl+alt+h by pressing that combination, then press Enter to set it.

You can also change the workbench.action.terminal.focus binding if you wish. I use ctrl+alt+j

That's all.