Close the All 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 last state of All tools pane when opening documents.

Select OK. Open a PDF document in Acrobat Reader, 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.