Refill A/C, where is the low side port located?

Being a 2019 that truck has 1234YF in it not 134A. As such you really should be using an AC machine to prevent any issues with discharging and filling the system as 1234 is very fussy about charge levels and trying to fill only on the low side generally doesn't work.
What is the reason for adding refrigerant? System was opened to replace a part? System isn't cooling and you have tested all other options? Just trying to avoid a couple items with these systems, I have seen people put 134A in them and that causes major problems as the two types are very different and once added the only remedy is a full system flush, replacement of the drier and many times the o-rings.