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:

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