I was wondering if there is an advantage to speedunning on a digital copy of smo or a physical copy of smo.

I'm not sure, but I know that on Mariokart 8 deluxe a digital copy has faster loading times than physical so it may be the same for Odyssey.

with the digital version, we gain about 30 seconds cause the loading is faster

I think it's closer to 15 seconds over physical, but yeah load times. Not a huge deal at a beginner-intermediate level, and even at a top level some still use physical.

Yes because Digital has faster load times