Make your own engine, open source it, get plenty of traction, then make money off it as its premier consultant, or have a team who specialises in porting, etc.
The first bit will take time. Or you might have a "hook" which speeds up the traction part a bit (like Bevy being made with Rust, I guess).
AAA game engines are really challenging, nowadays you are expected to process everything on GPU. You need to do realtime illumination and collisions in a very performant way. If you can do that, then you might have a chance to compete against industry beasts like Unreal.
Otherwise your best chance is creating a "game maker". A framework with editor that allows people to make simple to medium complexity games easily but won't require high performance. There are a lot of low skilled gamedevs that would love it.
The decent money could come from services you offer around the engine.
Didn't Unity and Epic both have a bunch of layoffs recently? Unity seems like it's circling the drain, and Epic is partially owned by Tencent, the Chinese gaming giant. Not sure how that translates directly into worklife stuff, but it can't be a good sign...
By contrast, Valve (Steam/Source Engine) is privately owned and always seemed like a great place to work? They're "always hiring", they say: https://www.valvesoftware.com/en/jobs?job_id=51
No.
[dead]
I have a friend who was making ~300k at Blizzard (after being there for a while and a number of promotions) working on engines, and another who made quite a bit more then that working on an engine for CoD.
The thing is, he likely could have been making 30-50% more if he was working at a FAANG type company in terms of where he'd likely slot in level wise.