I work on a mac, and have 'lost' the menu down the LHS of the screen. The Quickbooks help chat were completely useless. has anyone else had this problem ?

I've experienced this, too, Michelle.

The three horizontal lines (≡) beside your company name allows you to hide the tool bar. You might have accidentally clicked this option.

You can click it again to make the tool bar reappear. See the screenshot below.

It's also possible that cache files caused the issue. Cache can enhance QuickBooks processes, however, it can also cause unexpected issues.

We can do a few troubleshooting steps to get rid of this possibility:

1. Click Help at the top menu and select Reset App Data.
2. After that process, you can close and reopen the app.
   

If you're using a browser on mac, here's how to troubleshoot it:

1. Open a private browser and access your account again. Private browser still uses cache but won't store it on your browser.
2. If the left tool bar reappears, we can clear the cache storage of your regular browser.
3. You can also use other supported browsers. Each of it uses and stores different sets of cache.

Additional information about it would be much appreciated if you need more help with this.