Level up is one of the oldest gaming phrases, it's still used in RPGs when you quite literally level up, so no idea why it's made out like it's dead (I'm playing Witcher 3 once again, and just for an example I've searched witcher 3 level up, and every top article/video recommend in Google uses some variation of level up/levelling up). And I'm pretty sure 2020/2021 wasn't many years ago, and we're in 2022 and I'm seeing it being used when I searched it.
It was used in a gaming context, it's an active phrase. Whatever you want to say, its a gaming phrase that is still in use in gaming, it's absolutely fair use.