SinEt

Ok, so let's see the steps I followed.
 
1. Installed Armbian Unstable for OrangePi Zero2:
https://imola.armbian.com/dl/orangepizero2/nightly/Armbian_21.05.0-trunk.77_Orangepizero2_hirsute_edge_5.11.11.img.xz
 
2. Forced ethernet at 100 mbit/s, otherwise it did not work: added in /etc/rc.local
ethtool -s eth0 speed 100 duplex full autoneg off
 
3. Downloaded hexdump's precompiled kernel (derived from jernej's 5.11.0rc1 kernel):
https://github.com/hexdump0815/linux-mainline-and-mali-allwinner-h6-kernel/releases/download/5.11.0-rc1-stb-616%2B/5.11.0-rc1-stb-616+.tar.gz
 
4. Extracted the various parts and fixed the symlinks:
Image -> Image-5.11.0-rc1-stb-616+
uInitrd -> uInitrd-5.11.0-rc1-stb-616+
dtb -> dtb-5.11.0-rc1-stb-616+
 
5. Inside dtb-5.11.0-rc1-stb-616+, created a new folder "allwinner" and moved the 3 .dtb there; otherwise, initramfs would not find them
 
6. Rebooted. Voilà, we now have a working mainline-ish kernel (patched 5.11.0rc1) with USB support!
[ 57.289791] usb 2-1: new high-speed USB device number 2 using ehci-platform [ 57.454110] usb-storage 2-1:1.0: USB Mass Storage device detected [ 57.454976] scsi host0: usb-storage 2-1:1.0 [ 59.122397] scsi 0:0:0:0: Direct-Access Lexar USB Flash Drive 1100 PQ: 0 ANSI: 6 [ 59.124408] sd 0:0:0:0: [sda] 125038592 512-byte logical blocks: (64.0 GB/59.6 GiB) [ 59.125522] sd 0:0:0:0: [sda] Write Protect is off [ 59.125549] sd 0:0:0:0: [sda] Mode Sense: 43 00 00 00 [ 59.126563] sd 0:0:0:0: [sda] Write cache: enabled, read cache: enabled, doesn't support DPO or FUA [ 59.163290] sda: sda1 sda2 [ 59.168389] sd 0:0:0:0: [sda] Attached SCSI removable disk