A recurring issue (at least for users that utilize more than one keyboard layout or input source?!), is that Alt+Shift is a sticky setting for changing input source. That means, even if you change Gnome's keyboard settings to something else, like <Super><Space> (a popular choice, it seems), Alt+Shift still sticks! Which not only ruins using Alt+Shift+Tab, but also every other shortcut in all programs using Alt+Shift as modifiers, including IntelliJ (my main work tool). That sucks and is super-confusing.
Today I learned that this is caused by a setting that is stored outside of gnome's keybindings schema (org.gnome.desktop.wm.keybindings has the switch-input-source setting):
gsettings get org.gnome.desktop.input-sources xkb-options
['grp:alt_shift_toggle', 'grp_led:scroll']
Removing this setting "fixes" things (doing gsettings reset org.gnome.desktop.input-sources xkb-options), but why should I ever need to do so? Why can't simply Gnome clear this by default and use its own setting? This is so bad UX and almost seems like a glitch of some kind, but it seems as if it has been there for 4 years now, so in that case it should have been fixed. Is there any good reason for that behaviour?
Related
- https://unix.stackexchange.com/questions/45447/other-than-alt-shift-to-switch-keyboard-layout-any-other-xorg-key-combination
- Ubuntu 18.04 alt+shift+tab does not switch apps backwards
Ubuntu 21.10 distro upgraded from 21.04
Both the mechanisms you describe have their merits and complete each other, even if they don't always play well together.
However, I thought that bug #1762952 was fixed. Has something happened since then which makes the system define Alt+Shift by default again?