Small update on my research to make the image work with Beelink GT1:
After trying a few things, I eventually decided to start again from scratch with Armbian_20.05.1_Arm-64_bionic_current_5.6.0-rc7_20200404.img.xz. After installing, same problem on clean install. I then tried to go back to 20200331 version, which was previously working. To my surprise, and despite using the exact same image (clean format using balenaEtcher), it was also not working anymore ! I thought about an hardware problem, but rebooting on android emmc system prove me wrong as ethernet was there working fine. I then flashed back the SD to 20200404 and used Q201 dtb file. The eth0 interface is recognized but there are still errors in kern.log and the interface is still faulty (can't get an IP from DHCP nor connect to it when set statically):
root@hassio:~# dmesg -T --level=err,warn
[Wed Apr 8 17:02:39 2020] KASLR disabled due to lack of seed
[Wed Apr 8 17:02:41 2020] OCFS2 User DLM kernel interface loaded
[Wed Apr 8 17:02:42 2020] meson8b-dwmac c9410000.ethernet: IRQ eth_wake_irq not found
[Wed Apr 8 17:02:42 2020] meson8b-dwmac c9410000.ethernet: IRQ eth_lpi not found
[Wed Apr 8 17:02:42 2020] meson8b-dwmac c9410000.ethernet: PTP uses main clock
[Wed Apr 8 17:02:42 2020] dwc3 c9000000.dwc3: Failed to get clk 'ref': -2
[Wed Apr 8 17:02:43 2020] phy phy-d0078080.phy.3: unsupported PHY mode 5
[Wed Apr 8 17:02:43 2020] hub 2-0:1.0: config failed, hub doesn't have any ports! (err -19)
[Wed Apr 8 17:02:43 2020] mmc2: queuing unknown CIS tuple 0x80 (2 bytes)
[Wed Apr 8 17:02:43 2020] mmc2: queuing unknown CIS tuple 0x80 (3 bytes)
[Wed Apr 8 17:02:43 2020] mmc2: queuing unknown CIS tuple 0x80 (3 bytes)
[Wed Apr 8 17:02:43 2020] mmc2: queuing unknown CIS tuple 0x80 (7 bytes)
[Wed Apr 8 17:02:47 2020] gx-sound-card sound: ASoC: no DMI vendor name!
[Wed Apr 8 17:02:47 2020] panfrost d00c0000.gpu: d00c0000.gpu supply mali not found, using dummy regulator
[Wed Apr 8 17:02:47 2020] panfrost d00c0000.gpu: GPU Fault 0x00000088 (UNKNOWN) at 0x000000fcffbfffc0
[Wed Apr 8 17:02:48 2020] meson_vdec: module is from the staging directory, the quality is unknown, you have been warned.
[Wed Apr 8 17:02:48 2020] hci_uart_bcm serial0-0: serial0-0 supply vbat not found, using dummy regulator
[Wed Apr 8 17:02:48 2020] hci_uart_bcm serial0-0: serial0-0 supply vddio not found, using dummy regulator
[Wed Apr 8 17:02:48 2020] brcmfmac: brcmf_fw_alloc_request: using brcm/brcmfmac43455-sdio for chip BCM4345/6
[Wed Apr 8 17:02:48 2020] brcmfmac mmc2:0001:1: Direct firmware load for brcm/brcmfmac43455-sdio.amlogic,q201.txt failed with error -2
[Wed Apr 8 17:02:48 2020] bluetooth hci1: Direct firmware load for brcm/BCM4345C0.hcd failed with error -2
[Wed Apr 8 17:02:49 2020] meson8b-dwmac c9410000.ethernet eth0: PTP not supported by HW
[Wed Apr 8 17:02:49 2020] ext4 filesystem being mounted at /var/log supports timestamps until 2038 (0x7fffffff)
[Wed Apr 8 17:02:50 2020] brcmfmac: brcmf_fw_alloc_request: using brcm/brcmfmac43455-sdio for chip BCM4345/6
[Wed Apr 8 17:02:50 2020] brcmfmac: brcmf_c_preinit_dcmds: Firmware: BCM4345/6 wl0: Feb 27 2018 03:15:32 version 7.45.154 (r684107 CY) FWID 01-4fbe0b04
[Wed Apr 8 17:03:09 2020] process 'docker/tmp/qemu-check033460557/check' started with executable stack
[Wed Apr 8 17:03:12 2020] overlayfs: NFS export requires "index=on", falling back to nfs_export=off.
I've extracted the dtb file from the working Android system and from the 20200404 img and converted them to dts file. I tried to adapt some values in the ethernet@c9410000 {...} part to mimic what is in the android part, but this didn't help (in some cases, it created more errors). I'm really confused how as how to make progress on this, any kind of help would be very welcome (dts files in attachments).
android-q201.dts meson-gxm-q201.dts