For anyone who is concerned that this only applies to Toyota drivetrains (which was true for quite some time), Toyota made nearly all of their HEV patents (24,000 of them) completely royalty-free in 2019 [0].
At this point, I assume the only thing stopping manufacturers is their pre-existing investment in other technology.
[0] https://global.toyota/en/newsroom/corporate/27512455.html
From what I know (granted I’d rather have a bev, but alas) this also applies to the Honda hybrid system, I’m sure there are others.
Ford Kuga (EU) / Escape (US) is built from those patents. It’s basically a copy of Toyota’s hybrid system. And it’s actually quite great, until it catches on fire.