Honestly, I... don't have a clear idea how GER's RtZ works. So I'll take your words about GER's ability into mind, and the link too.
Still, tho... Saying that GER's mind is so built different to the point that it is immune to Type 3 MM is a stretch - cognition, by definition, means the mental action or process of acquiring knowledge and understanding through thought, experience, and the senses; so GER being an intangible spirit/stand shouldn't matter since it can think, which means, it should fall under the effect of Type 3 MM.
Heck, GER's stand physiology is probs enough to defend against Type 1 (Biological) & Type 2 (Mind Manipulation) since the former requires something a stand doesn't have (i.e, bodily parts) and the latter is something that likely needs layered NPI to affect a stand (Mind Manipulation) - but Pandora's Type 3 MM just requires Giorno/GER to perceive her to drive them mad.
It doesn't matter that the ones who were affected by Pandora's Type 3 MM hax were biological folks - they perceived her, so they turned mad. And Stand Physiology and their intangibility don't cover that - tbh, even if it does affect GER, RtZ is still a thing, but still Pandora'sType 3 MM is passive, it would immediately fall under her hax again, and GER would break out of it with RtZ, and fall under it again, yada yada.
Like, this is a passive ability, after all. As long as Giorno/GER can perceive Pandora, they'll be under her Type 3 MM. Negating them being under its effect won't stop her hax from immediately affecting them again - to beat a passive ability, you need to be immune to it or have a huge resistance towards it or have a rating of immeasurable speed to not fall under its effect.
... Also, this isn't accounting for Pandora's own causality hax, which will likely prevent GER's attack from reaching her by YEETing Giorno somewhere or making it so that GER's attacks never happened, and since GER's actions didn't happen, she never got hurt. Probably won't work, but I have to mention this.
Honestly, the only reason I am here is cuz of Pandora's Type 3 MM, this would be a clear STOMP for Giorno, otherwise.