What are some of the most impactful novel inventions in the past 20 yrs?

In terms of raw impact, probably smartphones and social media. (No, these aren't strictly new within the last 20 years, but approximately so, and most of their impact came from their widespread adoption within the past 20 years -- roughly since Facebook and the iPhone.)

A lot of other innovations within the last 20 years are downstream of these -- e.g. no Uber without smartphones.

Whether these had a net positive impact is a totally different question. Smartphones arguably enable a totally different relationship with the physical world: effortless navigation in unfamiliar places; dynamic social interactions in the real world, etc. And while we all partake of this to a certain degree, it seems to have been offset to a large extent by the negative influence of living more online.

Beyond that it's hard to think of inventions within the last 20 years that have really changed our lives. Personally if I woke up tomorrow and was back in a world with 2003 technology, I'd probably feel minorly inconvenienced, but not fundamentally worse off. (Admittedly I'm a fairly unsocial person -- the past 20 years of tech didn't do much to change that.)

Impactful? Smartphones aren't "completely new" but are in the process of destroying free societies by allowing total surveillance and total control.

Not new but incremental advances in tech has allowed for

1. Solar power to become economical

2. EV's to become viable

3. Smartphones to become very advanced and cheap

4. Electric motors to become small and efficient enough for home/commercial drones

5. Advances in heat pump efficiency

6. DC inverter based heating/cooling solutions

You didn't say whether that impact was positive or negative so I'll take a stab at Social Media in general and the negative impacts. Its more of a conceptual invention piggybacking off the internet. I keep seeing headlines indicating studies are showing teen girls mental health is severely declining when they are active in social media X hours per day. Then there are societal impacts of being an enabler for entities to push whatever propaganda (aka misinformation on purpose) fairly easily. Now with a surge in AI/ML advancements I suspect it will get worse.

In my opinion any positive impacts (are there any?) from social media are small in comparison and not worth it.

Dungeons and Dragons 5E. A huge step up from 4E.

iPhone

mRNA vaccines

Chatgpt

Cryptocurrencies.