After looking at the code and checking the Teensy 4.1's processor datasheet, it is known that there are edge interrupts on a row of GPIO pins. It means, if any pins at GPIO6-9 are changed, it triggers an interrupt.

 I'm suspecting that the polling of the address lines by Teensy couldn't catch up with the speed of the switching addresses at the NOAC. Having the pin change interrupt makes it easier for the NOAC to catch the instruction that is fed from the Teensy pins.

And... yes, there's the game menu, and it jumped into the test screen when I hold the A + B before the thing starts:

Unfortunately, there are limitations - the Teensy needed to be overclocked to 912MHz to do this successfully, and a heatsink is required. I am now figuring a way to have a fan to blow on the heatsink, and also to write up short pieces of 6502 code to make it run on that NOAC. 

And here's the Github page if you are interested in replicating the project.