Blablabus

The buses in France (BlaBla, Flixbus, others) have worked well for us in and out of Chamonix. We booked through the Omio app. There are a number of bus services between Chamonix and Geneva Airport and our Chamonix hotel suggested one that scheduled its runs whenever it had most of a van full rather than on a set schedule (It was, of course, a bit more expensive. I think it makes most of its money moving skiers back and forth during the winter). There are bunches of hotels near the Geneva airport, just pick one you like on sites like Booking.com. There are not many restaurants right outside the airport however.

We took BlaBla from Annecy to Chamonix a couple years ago when transport was just getting started up again after COVID. It was our only real option. It got us there at 11 and the departure for return for Annecy was 3.
https://janettravels.wordpress.com/2023/03/27/quick-trip-up-the-aiquille-du-midi-chamonix/
It was fine. Nice bus, on time. Our only hicup is that while the bus going was orange with blablaCar on the side and easy to spot, the return but was a white bus apparently rented from some other company and there was not even a card in the window indicating its destination. We would have missed the bus if I had not asked the bus driver if he was the bus to Annecy.

I would use them again after our experience. (and with a name like BlaBla. I did have my doubts. I only agreed to use them when I identified a backup train route in case we got stranded. The bus was about an hour -- the train was very convoluted and so we were happy to not have to go to plan B.

Note that BlaBlaCar announced 15 days ago that it will cease its BlaBlaBus service by the end of 2026 due to a lack of profitability.

https://www.voyages-d-affaires.com/en/blabacar-bus-will-soon-be-finished