There are fanfictions that rewrite certain arcs in the Tower of God story. Like if the Crown Game arc had different rules or participants. This can add a fresh perspective to the events that we already know from the original series. These types of fanfictions often attract readers who want to see a new take on familiar plot points.
Well, there are also some dedicated light novel reading websites. However, be cautious as not all of them are legal. For the Tower of God light novel, if you're in Japan, local bookstores would be a great place to find physical copies which might come with some exclusive bonuses.