@obsolete maybe should have mentioned that :)
ok so that is surely your issue. you're using hdmi_safe=1, which forces
hdmi_group=2 hdmi_mode=4which means 640x480. it may be that your TV puts borders on such a low resolution, and there's nothing you can do about that after the fact.
i would change hdmi_safe=0 and manually edit hdmi_group and mode to something sensible for your TV. probably:
hdmi_group=1 hdmi_mode=16or
hdmi_group=2 hdmi_mode=82btw config_hdmi_boost=9 does nothing on a pi4.