I will find the Holy Grail (no SMS or registration required).

Do you mean the exact location where it is buried, or the exact area where it is buried?
If it's the latter, then it's not difficult to determine it by the mushroom (and it's good if there is one), and sometimes you need to open several obelisks to find at least some clues.
P.S. If you show the exact location, I think all the excavations will stop, which many already consider to be cheating.

The exact location of the puzzle. I don't think it's possible to indicate the exact location of the Grail without seeing the cross, but there are some patterns, and they have probably already been noticed by excavation enthusiasts. This is a separate topic about which cells to check first, i.e., where the probability is higher and where it is lower. But for this, first, you need to determine the exact location of the puzzle and its center, and then make some offsets from this center.

Regarding the mushroom specifically (and it's good if there is one) - the point of the topic is not just to find the Grail once or find it in half of the cases (this can be done even with just one obelisk), but to do it always and without errors with the specified number of obelisks.

Can I opt out?

Participation is obviously voluntary and currently open:-) But seriously, it would be interesting to get the most difficult case from the excavation master.

And in general, I am not only not against selecting tricky cases, but even the opposite - the more valuable the test.