HKS silently discontinued their “catless” downpipes in the U.S. around 2021 for mentioned reasons above.
The loophole is that it doesn’t apply if you never take it off private property.
You can't modify the factory emissions output to go below the required output.
People like the Diesel Brothers from the Discovery Channel settled for like $3 million USD with the EPA for selling and promoting emissions defeat devices like tunes and straight pipes.
I or a family member has acquired a few vehicles where the catalytic converter was cut out by thieves, and I've done both so I can tell you from experience that it's the difference between $15 and $800 (parts and labor).
Having grown up extremely poor, sometimes families make those decisions because they don't really have a choice. Thankfully nowadays I do so I tend to err on the side of being a good citizen but personally will not judge anyone who choose s to weld a pipe in place rather than spend the exorbitant amount necessary to replace it, especially considering it might just get stolen again.