From March 2000 to October 2002 the Nasdaq-100 fell −83%. A 3x fund fell −100.0%. TQQQ didn't exist yet, but the reconstruction tracks the real fund closely, and the result is the same either way: almost nothing left. It never got back to its March 2000 level.
The 2022 bear market was the first the real fund lived through. From the Nasdaq's peak at the end of 2021 to its low in late 2022, the index fell −35% and TQQQ −80%. TQQQ didn't regain its 2021 high until December 2024.
These are the two periods that decide whether holding 3x is survivable. The signal sat out both almost entirely: it was in TQQQ for 0% of the dot-com decline and 0% of 2022. In 2022 that didn't save as much as it should have, because the Treasuries it held fell too. More on that in when Treasuries hedge. Replay either period day by day