As I say, "can't do encounter RNG at all" doesn't mean "no tool exists yet but maybe". Certain stuff from LGPE onwards (notably including
all Pokemon encounters in SV) uses cryptographically secure RNG, which is
completely impossible to predict and should never be cracked; this includes IVs. The most you can get is Snacksworth legendaries having no guaranteed IVs due to a bug, meaning you can just reset for stuff like eg. 0Atk 0Spe Lunala (and just Bottle Cap the rest), but again no possible guarantees. You can also """guarantee""" Tera Raid IVs because you can save the raid seeds apparently (see some threads in Wi-Fi subforum), but this probably isn't what you're looking for since you aren't controlling them in the first place.
See this playlist. TL;DW you need some sort of camera setup (either capturing Switch output directly or using a webcam linked to a computer) and a Python script to track NPCs blinking in order to find your position in the RNG.