Yes , waterproofs.
Maybe some mud tyres. (Hillbillys seem to work well).
I was in Les Gets in August a few years back and it was like riding inside a dishwasher.
Rather generously, I thought, the big local bike shop was selling builder’s one piece all plastic overalls at what seemed a fair price. Kinda gives an idea of how wet it can be. I bet they could have got €40 a set if they’d asked it.
Maybe visit screwfix for a coverall hit if you’re uplifting. Its been wet this year according to a pal in Cham, so they might have run out! She recommended Les Gets, new mellow trails she said.
Folk were hosing each other off with the bike wash. We gave up once drenched to be honest.
I’m in Les Houches next week and I guess it’ll be similar.
Enjoy, The Alps are wonderful, wet or dry.
N