footer layout (/clients/base/layouts/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 (/clients/base/layouts/sidebar-nav) as part of its metadata array. The last sidebar-nav-item-group layout element named sidebar-nav-item-group-bottom. That layout element is Sugar's new redesigned footer.
Note: sidebar-nav has different states that must be handled when refactoring your footer buttons as well as secondary actions (submenu). Use this opportunity to 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.