12 speed cassette touching spokes
Sounds like the easy solution is going to be get an extra long lockring. Wheels Mfg and another company I can't remember both used to offer them. I believe current Chris King ones are longer than average but I couldn't come up with a number.

Double check your wheel dish is right, because if it happened to be way over to the right, it could cause or contribute to this problem. But it would have to be extreme and you'd probably notice.

Another approach would be lacing tricks. I'm assuming it's 3x now. FH-M756 is the sort of hub where the shell has a fairly large smallest inscribed diameter and so torsional loads can be handled all by the left flange if you want, meaning you've got all sorts of options for half-rebuilding it, but not knowing where exactly the rub is I won't speculate what would be best in terms of being able to solve the problem while giving up the least bracing angle. The lower a cross number you choose, the further away from the hub the cross will be, and it's usually the cross area where you don't have the clearance you need in these situations. Just making it 2x or 1x on the drive side could very well solve the problem. There's also options that involve moving some or all of the drive side spokes to being heads-out, which also threatens to reduce the lateral strength of the wheel.