For Teensy 4.0 core code, I believe that the only thing from not using the DSB will be just that sometimes the internal ISR is called but it does not find any GPIO pin which triggered the interrupt, so simply the ISR does nothing. In other words, just a little bit of computing power waste For most purposes, it should be fine when the task is not really time-critical (but my case was indeed.) On the other hand, I guess adding DSB to the internal ISR of the Teensy 4.0 core may not harm anything

I will read the sections in the ARM manual on the DSB, and the T4 beta thread. Thanks a lot for the wonderful and fast help!!!