the scroll limit is actually int, so it can be set between –2147483648 and 2147483647.
but in editor, range controller provides -65536 to 65535 which can be satisfied most of games.
if it provides whole range of int, you can't control the number with range controller.
if you want to set the limit value larger, you can do it with script.
print("limit right = ",get_node("Camera2D").get_limit(MARGIN_RIGHT))
get_node("Camera2D").set_limit(MARGIN_RIGHT, 6553500)
print("limit right = ",get_node("Camera2D").get_limit(MARGIN_RIGHT))
it prints
limit right = 65535
limit right = 6553500
it would be better if editor accepts lager value when set large number manually.