It’s more than you think. I work with the MSP430 microcontroller, which is capable of a sleep current of 40nA @ 2V, full active mode at 140uA/MHz with all onboard peripherals turned on. With this you could achieve almost a 20% on-off ratio with a 1MHz clock, or keep it in active mode all the time at ~150kHz, which is sufficient for many embedded sensor applications.
GTA online took ages to load, like 10+ minutes on some machines. One guy got really annoyed and investigated. It turned out to be loading a single 10MB JSON file in an incredibly inefficient manner. The JSON file contains about 60,000 items and they need to extract each item from it, but every time they look for the next item they start from the beginning of the file again, despite already knowing where they found the previous item! All the entries in the JSON list are unique, but the code also checks for any duplicate entries, of course it’s also done in the least efficient way possible requiring 1,984,531,500 comparisons for something that has no effect. Not only did this one person find these problems but he also implemented a fix that reduced load times by 70% as a result, shaving off more than 7 minutes of load times for some machines. The fact that Rockstar didn’t notice this is frankly shocking and speaks to the fact that they really just don’t care.
https://nee.lv/2021/02/28/How-I-cut-GTA-Online-loading-times-by-70/
The MSP430 is just the chip I happen to use at work, if you’re not convinced you could try looking for an actual ultra low power chip, I found the STM32U0 at 70uA/MHz and the STM32U5 at 16uA/MHz in the first result.
Even ignoring selecting a more efficient micro, a smattering of tiny ceramic caps will buy you a few hundred microjoules for bursts. If you’re already operating at 2V you can get a 6V rated 100uF cap in a 1210 package - and that’s after considering the capacitance drop with DC biasing. Each one of those would buy you 200 microjoules, even just one ought to be plenty to wake up for a few tens of milliseconds every second to get a reading from some onboard peripheral (as an example) then go to sleep again.
For sure, you’re not going to be doing any heavy lifting and external peripherals could be tricky, but there are certainly embedded sensor use cases where this could be sufficient.