This, of course, is only possible thanks to incredible work of volunteers from Asahi Linux and OpenBSD.
The installation is relatively straightforward:
1. Resize your MacOS drive to have enough space for a new OS,
2. Get Asahi Linux installer,
3. Install UEFI-only,
4. Get OpenBSD install79.img and record it on a USB stick (with dd or whatever)
5. Boot Asahi UEFI, it will pick up the stick
6. Install with default settings (skip configuring the network)
7. Mount /dev/sd0i as /boot, find FIRMWARE.TAR on the disk, unpack WiFi firmware to /etc/firmware/apple-bwfm
8. Configure network as usual, install whatever stuff you want, be it xenodm, xfce4, firefox-esr, chrome, etc etc
9. Bonus: configure GDK_SCALE=2
10. Bonus: configure touchpad through /etc/wsconsctl.conf
11. Bonus: configure firefox unveil through /etc/firefox
One scary part in this step is getting the disk partitioning right. Asahi manual and OpenBSD manual say that it is safe to use "Whole disk" setting, as it won't damage the MacOS partition required for the computer to function. The manual does not lie here.
Fdisk tool will show the full size of the SSD on the computer, but OpenBSD installer will still only use the part of the disk that is available for Asahi when "whole disk" setting is chosen.
@ejstacey it looks like the full charge should last ~3 hours, which is not impressive at all. But I haven't fully measured it yet.
It won't be super cool because closing the lid won't make the laptop sleep, probably...