I used to develop SSD firmware and one of things I worked on is making it robust to power failure. The power supplies have lots of capacitance so the voltage drop was slow so we would use a special test board that would disconnect from power and discharge fast to test it.

And more concurrent writes.

But I think ext4 will only let things appear there if you change some default flags.

Umm .. how about a Raspberry Pi Zero 2W powered by a 2000MaH " lipstick style" powerbank?