It’s not really that great of a business.

Epic is estimated to have made $275M revenue on Unreal engine in 2023, vs $4.7B on Fortnite

Unity made $614M revenue on engine & tools in 2024, in ads and monetization they made $1.2B

These are stable industry standard engines, if you start work on your challenging engine today it’ll take years to develop, gain game-developers interest and trust. And still you’re competing with giants that use their engines as loss-leaders.