What exact command did you try?

Maybe you don't know, but you can add your own tools in the preferences.

Will be fixed in #20105.

To check out a branch by typing the name, you can use Ctrl+P popup.

Set the low-level property repository.suggestMostAppropriateGroup to false.

Would you mind invoking an extra action in the Commit view (or dialog) to trigger invoking the .git/hooks/commit-msg script?

In the next build there will be a low level property to show the path, too.

Works fine on our Linux machines (Ubuntu, Manjaro - both with Gnome desktop).

Drag the commits right beside each other, select them and invoke Squash.

Please describe your workflow in more details.