In my case, I had accidentally changed the setting for viewing files in tabs and didn't know where to look to change back to the behavior I was used to, i.e., double-clicking on the files name in the file explorer pane (typically on the left-hand side) to open the file in a new tab.
There is a setting to check or uncheck "enable tabs".
In Visual Studio Code 1.77.3, you can click on the three dots on the right-hand side (see the image below).

Note:
Full version information of my Visual Studio Code installation:
- Version: 1.77.3
- Commit: 704ed70d4fd1c6bd6342c436f1ede30d1cff4710
- Date: 2023-04-12T09:16:52.732Z
- Electron: 19.1.11
- Chromium: 102.0.5005.196
- Node.js: 16.14.2
- V8: 10.2.154.26-electron.0
- OS: Linux x64 6.2.0-20-generic snap
- Sandboxed: Yes
"window.restoreWindows": "preserve",github.com/microsoft/vscode/issues/36964