HALO INFINITE BETA

who tells me in which section I can comment on the bugs of the halo infinite beta

I don’t think there is a designated forum, you’ll probably want to send in a ticket through the Halo Insider support page.

On the websites’ top navigation bar:

Support → Halo Insider Support → Halo Infinite → Known Issues, scroll to the bottom & click submit a ticket

This link may or may not work for you:
https://insidersupport.halowaypoint.com/hc/en-us/articles/4403344734612-Known-Issues-Halo-Infinite-Technical-Preview-Flight

If you are encountering issues during the flight, please refer to the known issues list on https://aka.ms/HaloSupportInsider and submit tickets for issues not present.

For general feedback that is not a bug or issue, feel free to use the pinned feedback threads at the top of the Halo Infinite forums
https://www.halowaypoint.com/en-us/forums/29568daf8cd14083bd1b70a810bf3581/topics