Which Pokemon Go fast move is this from Rocket's Porygon/Porygon2/Porygon-Z?
Solution 1:
Opposing Hidden Power in a Team GO Rocket battle (or raid) is always Fighting-type. It is also bugged in that it states "not very effective" based on whether the opponent resists Normal-type or not, not the actual type of the move (in fact, it can never be Normal-type). It also always has the same Electric-type animation regardless of its type (thank you Wondercricket). And it can deal a large amount of damage to Tyranitar because it is 4x super-effective, whereas none of Porgyon's other moves are super-effective.
So the move is Hidden Power Fighting.