footer has been completely removed on version 12.3+ and will no longer render any contents from this layout and its component views.
It's redesigned replacement is in sidenav-bar, the last sidebar-nav-item-group metadata layout named sidebar-nav-item-group-bottom.
Note: sidebar-nav has different states that must be handled when refactoring your footer buttons as well as secondary actions (submenu).
Improve your user’s experience by avoid opening unnecessary popups or BWC Window to detect next steps, use your button’s submenu to provide a better experience and navigate to a different page from there.
Follow this throughout example to Move your Footer Content to Sidebar-Nav.