The Romans conquered the Greeks militarily, but the Greeks conquered the Romans culturally. Saying "octopi" indirectly attempts to not acknowledge that.
https://youtu.be/J7E-aoXLZGY?si=2D27LKx73o0UOXoo
In short, context, convention, and circumstance are all. Long live the solitary octopi.
Octopi is correct, in that it is an english language plural for octopus. It is not etymologically sound, certainly, as it's a latinate plural on a greek root.
So anyone telling you that any other form is wrong and insuating that 'octopi' is more correct is certainly asking to be mocked. But as we don't really do '-podes' in english, and "Octopusses" is a bit of a mouthful, I think we can accept any and all as more or less equally cromulent.
Not to argue against this, I'm just wondering how many Greek -foot words I can think of.
That said, wikipedia mentions antipus or antipous may have been correct before the 16th century, and antipode is likely a sort of reverse de-pluralisation.
I can't say I'm familiar with many of the other -podes words: https://www.merriam-webster.com/wordfinder/classic/ends/all/...
They seem largely to be part of scientific species names. 'pods' is more natural feeling. Tripods, bipods, gastropods, cephalopods!
"Octopuses" is both understandable and correct etymologically since "octopus" is a normal English word.
Personally I'll use octopuses, just because I once confused octopi as a word for another species of the family octopodes belong to. Now I know it's a common plural, but it didn't sound like a plural to me back then.
I'd prefer to use octopodes, but I feel like this can too be confused with another species, and I don't want to sound all smart in saying it's actually a plural. Octopuses bypasses all that confusion, and probably everyone will understand that it's the plural of octopus, albeit some might have doubts whether it's the correct form or not.