2022 M3 LR. I've hosed down the car and driven in pouring rain as well, and I've never before noticed any water in the frunk. I'm thinking it was the 8-12" of water I had to motorboat through to get in and out of the Toot 'n Totem parking lot right on US-287. Some must have splashed up through the frunk latch, but I haven't take the frunk apart to check to see if it's sealed in that area. I didn't discover the water until a couple days later, and it was only in the most forward part of the frunk, below the depth of the ribs, so I was able to put in some groceries without them getting wet. There was some water in the tow eye slot as well, so when I got home I dried everything off and it only took a couple of shop towels. I should have take a photo, but I was a dum-dum and didn't.
I left the frunk lid open (in the garage), and the next day I noticed some water in the driver's side screw hole that hadn't yet evaporated. This time I took photos:
Photo 1: frunk all dry (except you can actually see a reflection on the water in the driver's side recessed screw hole)
Photo 2: passenger side screw hole - dry
Photo 3: driver's side screw hole - still wet after 4 days
Photo 4: frunk latch area - suspected water entry point when motorboating through high water