If the “Apps” option on the left side of QBO Accountant client file has disappeared and need to get it back, here is the temporary workaround solution.
From the client’s home page > Go to Gear (upper right corner) > Settings > Quickbooks Labs > Turn on “Alternate Navigation with Centers” > Click done. Refresh the home page. You should see the “Apps” on the left navigation bar. Unfortunately, you’ll have to do the same for each client company when needed.