RD-M5120 spec states max sprocket 46T for 1X10/11 and 42T for 2X10/11.
The issue comes in capacity, which is listed at 41T. If you have a 24/36/48 triple crankset, your rear derailleur capacity requirement is (48-24) + (42-11) = 55T
What this would mean functionally, would be that your derailleur would not be able to keep enough tension on the chain when you’re in combos near 24Front/11Rear, which you should never be in.
I ran a long cage 2X10 rear derailleur with an 11-36 cassette for years with no problems, even though the capacity requirement wasn’t met.