This guide states a Frigibax can be found via “trade/migrate from another game.” However, I don’t know exactly what that means. Is this referring to a different generation entirely?
Hey there. I was able to verify that they can be found at both:
Glaseado Mountain (I found them north-by-northeast of The Higest Peak in Paldea, and I have seen them elsewhere as well).
Dalizapa Passage at various points along the path.
This matches the Bulbapedia page.
The Pokemon DB Scarlet/Violet location guide is currently very inaccurate; most locations are incorrect. As of now, I would use Serebii or YouTube to find specific Pokemon you're looking for.
According to Serebii's Interactive Map, Frigibax can be found anywhere in the Cave or Snow biomes at a very low encounter rate.
Hope this helps and ask if you need more direction!