I don't like using the term innovation. That word has led us to the sate we are now, an industry full of decline. As JarlFrank said, if you want to "innovate", expand and improve upon the key aspects of what makes a great RPG.
Using a game like Underrail as an example, innovation would be to expand the noncombat portions of the game. This should be done by making more quests that aren't expressly combat related as we saw in the "secret" quest line. How about some quests that introduce puzzle mechanics to the game which will lead to more lore or useful items or really anything. There is no more innovation that needs to be added to the game then that and new locations, quests, and perhaps building upon the existing systems.
Let's pivot to games like BG or IWD. I want a new module, with new quests, locations, and some tweaks to the engine. Disco Elysium? Add some more "combat-like" encounters and give us a new story with a new setting.
It's not rocket science, and it's precisely because of "innovation" that we've had so much decline. I think a big part of this is because it's difficult to expand on something you've already built. When you're just starting out planning a game, the writing, the encounters, everything, is fresh and new and you're full of ideas. The second time around, you've already implemented so much of the good shit, it's hard to think of new ways to implement them. Instead of biting the bullet and figuring it out, people try to cover up these holes with "innovation" out of sheer laziness and creative bankruptcy. Here's hoping something like Underrail: Infusion, will prove it can be done.
EDIT: I haven't played it yet, but judging by the positive reviews, KotC 2 went ahead and did exactly this.