Since this is HN, I'll go with the most obvious: Software development. Unsustainable, speculative growth through the COVID-19 period, but on the other side relatively slow decline.
Nobody pays attention to things aligned to the fundamentals. When people are crying that there is a bubble, it is a bubble. Plain and simple.
We know for certain it was a bubble as non-bubbles have sustainable growth. As all the software developers now struggling to find work will be happy to tell you, the growth wasn't sustainable. The proof is in the pudding.
> How do you prove that software development is a bubble?
By looking at the software development market. How else would you do it? Salaries rose sharply from 2020-2023, but then plateaued and are now starting to decline. Slowly, however. It did not crash. It ticks the boxes: Rapid price appreciation, speculation, a disconnect from fundamentals, widespread media attention, and an eventual correction.
> Stock prices are at all time high and continuously growing.
If we're sharing random facts: Global average temperature is also at an all time high and continuously increasing.