For SWSH, any grass encounters, overworld encounters, roaming encounters or fishing encounters, has a known PID IV relationship, that you cannot just hack randomly. (There are a few exceptions, which you can read in Anubis's gist linked below)
Detection for that has been implemented into PKHeX. Legality report will show "Encounter Type PID mismatch".
Data that has a correlation presently: EC-PID-IV-Height-Weight (all chain generated from one encounter seed)
While it's possible to reverse the Encryption Constant to find the seed and then calculate what the results of that encounter would be, there's presently no public method to bruteforce the stats you want.
A wrote a tool to try to search for the stats a user may want, but do note it might take a while..
There's also no guarantee that every seed is legal (we don't know yet), but that is something we may find out in the future..
[I mentioned seed because the program just goes up by one seed per search]
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More info if you want (tweet plus link to gist): https://twitter.com/Sibuna_Switch/status/1379326888674463750
PKHeX's implementation of legality checking (if you can read C#): https://github.com/kwsch/PKHeX/blob/master/PKHeX.Core/Legality/RNG/Overworld8RNG.cs
Tutorial to obtain legal overworld8 details: https://projectpokemon.org/home/tutorials/save-editing/using-pkhex/pid-mismatch-origin-game-swsh-r114/