Okay, now I got things up to the 21 version. New problem. I cannot resize the overlay partition the way it is described in here (https://openwrt.org/docs/guide-user/installation/openwrt_x86#resizing_f2fs_overlay). I have only a few megabytes for installing python before it is full. The problem comes at the step:
root@OpenWrt:~# resize2fs /dev/sda2
resize2fs 1.45.6 (20-Mar-2020)
resize2fs: Resource busy while trying to open /dev/sda2
Couldn't find valid filesystem superblock.
The method described did work in the previous 19 version.
I updated with the openwrt-21.02.0-rc3-x86-64-generic-squashfs-combined.img.gz file