The selection model is unfortunately a bit broken. For example shift+control+arrows and shift+down doesn't work. I believe the problem is that selection with shift isn't written to compose with other navigation.
(I once wrote a hack for Linux that opened a connection to the X server and used the xkb -- X Keyboard Extension -- protocol to get info about the shift/control/etc state in order to synthesize shift+arrow and shift+control+arrow keycodes. It worked almost perfectly with a local X server.)
just checked the ctrl+thift+arrow keybind, works on alacritty but doesnt on kitty.
just checked the ctrl+thift+arrow keybind, works on alacritty but doesnt on kitty.
and shift+up/down works on both