I'm waking up this thread because this silly bug is still not fixed!
I'm running Start11 version 2.56, Windows 11 Pro, Version 25H2, OS Build 26200.7462
I've just installed SoftMaker Office. In the Start11 start menu, it does not appear under 'All apps'. In the Windows 11 start menu it does appear under 'All'.
Also, a new detail: even though it does not appear under Start11 'All apps', typing 'Softmaker' into the 'Search Apps and files' box DOES find it.
A reboot fixes the bug.