Close the Tools pane in Acrobat Reader

Choose the hamburger menu   (Windows) or the Acrobat menu (macOS) > Preferences.

In the Preferences window, choose Documents, then select Remember current state of Tools pane.

Select OK. Open a PDF document in Acrobat Reader, and then collapse the All tools pane.

Quit Acrobat Reader and open it again.

Acrobat Reader now maintains the last state of your All tools pane. If it was collapsed or expanded during your previous session, it stays in that state upon your next launch.