Hi! I've been playing the fishing minigame every time I can for a while, but I just can't seem to crack a strategy on how to get the actual prize. The closest I get is saying "If only you'd gotten a bit closer" and I was wondering if anyone has a strategy for it 😭 Thank you so much!

There isn't.

Been here for 18 years, never gotten the treasure, and have been trying any time I can in the hopes for the achievement. So I'm not holding my breath anymore in hoping I'll ever get it...

while you can be strategic about picking spots in relation to other spots to narrow down the general area based on the clues, there's no strategy for actually finding the treasure itself, no. it's random down to the pixel so you really just have to get lucky.