I use workspaces a lot and it is super annoying when I open text-editor and instead of opening a new window on the same workspace I get jumped to the workspace where text-editor is already running, and it opens a new tab. This is a known issue

Initially I thought I had fixed this by changing my keyboard shortcut to include the --new-window agument, however that was only half the solution. Opening a file which opened in text-editor had the same behaviour.

The fix for the 'open with' problem was to edit the .desktop entry. Specifically /usr/share/applications/org.gnome.TextEditor.desktop, or actually it's better to make a local copy in ~/.local/share/applications/ and edit that.

The line which needs changing is Exec=gnome-text-editor %U needs to change to Exec=gnome-text-editor --new-window %U. After that run update-desktop-database ~/.local/share/applications.