Why the script of filtering doesn't work

I made a field search filter before and it worked. but in this particular situation, it doesn’t work. I added a custom checkbox for the user doctype that checks if it is a technician or not. and in another doctype, I made a link field that links a technician user (filtering those who are technicians). however, the script that does the filtering doesn’t work and it shows all the users.
The code:

The result: (Note that only t1 and t2 are technicians)

I am not sure why you are saying that filtering is not working.
But according to my understanding filter seems to be working for if is_technician equals true.

Please correct me if I am wrong somewhere.