Need to check…but if there is someone with a working build environment this is easier for me 
Installed ubuntu 24.04 today (spare OS to my configured ubuntu 22.04) on laptop 
I hope i can still download the packages via debootstrap…support of ubuntu 18 was till last year
2023-05-01 Reflect lunar release, add mantic, remove bionic.
Bionic is u18
But nethertheless,i try to do when i’m at home later…
chroot worked…this is how i did it (ubuntu 24.04):
apt update && apt install debootstrap
mkdir u18-amd64
#mount -o remount,exec /media/frank/data_ext
debootstrap --variant=buildd bionic u18-amd64
mount -o bind ../git/BPI-R4-MT76-OPENWRT-V21.02/ u18-amd64/mnt
chroot u18-amd64/
apt update
apt install gcc-aarch64-linux-gnu u-boot-tools bc make gcc ccache libc6-dev libncurses5-dev libssl-dev bison flex
apt install gawk unzip wget python3 python3-distutils rsync file
adduser pi
su pi
cd /mnt
make menuconfig
make -j8
pi@frank-u24:/mnt$ ls -lh bin/targets/mediatek/mt7988/
total 842M
-rw-r--r-- 1 pi pi 19K May 1 15:37 config.buildinfo
-rw-r--r-- 1 pi pi 355 May 1 15:37 feeds.buildinfo
-rw-r--r-- 1 pi pi 136M May 1 16:10 kernel-debug.tar.zst
-rw-r--r-- 1 pi pi 110M May 1 16:11 mtk-bpi-r4-EMMC.img
-rw-r--r-- 1 pi pi 82M May 1 16:11 mtk-bpi-r4-NAND.img
-rw-r--r-- 1 pi pi 110M May 1 16:11 mtk-bpi-r4-SD.img
-rw-r--r-- 1 pi pi 65M May 1 16:11 openwrt-mediatek-mt7988-BPI-R4-EMMC-initramfs-kernel.bin
-rw-r--r-- 1 pi pi 72M May 1 16:10 openwrt-mediatek-mt7988-BPI-R4-EMMC-squashfs-sysupgrade.bin
-rw-r--r-- 1 pi pi 65M May 1 16:11 openwrt-mediatek-mt7988-BPI-R4-NAND-initramfs-kernel.bin
-rw-r--r-- 1 pi pi 75M May 1 16:10 openwrt-mediatek-mt7988-BPI-R4-NAND-squashfs-factory.bin
-rw-r--r-- 1 pi pi 72M May 1 16:10 openwrt-mediatek-mt7988-BPI-R4-NAND-squashfs-sysupgrade.bin
-rw-r--r-- 1 pi pi 65M May 1 16:11 openwrt-mediatek-mt7988-BPI-R4-SD-initramfs-kernel.bin
-rw-r--r-- 1 pi pi 72M May 1 16:10 openwrt-mediatek-mt7988-BPI-R4-SD-squashfs-sysupgrade.bin
-rw-r--r-- 1 pi pi 15K May 1 16:11 openwrt-mediatek-mt7988.manifest
drwxr-xr-x 2 pi pi 16K May 1 16:11 packages
-rw-r--r-- 1 pi pi 1.6K May 1 16:11 sha256sums
-rw-r--r-- 1 pi pi 12 May 1 15:37 version.buildinfo
i guess mtk-bpi-r4-SD.img is the right file…uploaded my build-environment and the SD image on my gdrive
Just saying, your lives would be much easier if you would either use GitHub actions or a docker container. Always a fresh checkout, so no issues with old files breaking things. And no pollution of your host OS with tools you might not need or need newer versions of.
I will share my GitHub repository in a couple of days. Just need to finish the configuration for the OpenWrt “from source” build. Currently I only use the imagebuilder for OpenWrt.
For compiling this repo this was easiest way…normally i have the tools installed…only because it is fresh install of ubuntu 24.4 i needed debootstrap. Most things were in the chroot. And all now need only unpack the tar.gz,mount their git repo in (or clone inside) and running make.
Now i try to load kernel with initrd instead of flashing image…lets see if this works…
seems this file is the right one:
$ dumpimage -l openwrt-mediatek-mt7988-BPI-R4-SD-initramfs-kernel.bin
FIT description: ARM64 OpenWrt FIT (Flattened Image Tree)
Created: Wed Apr 24 15:22:57 2024
Image 0 (kernel-1)
Description: ARM64 OpenWrt Linux-5.4.260
Created: Wed Apr 24 15:22:57 2024
Type: Kernel Image
Compression: lzma compressed
Data Size: 67256276 Bytes = 65679.96 KiB = 64.14 MiB
Architecture: AArch64
OS: Linux
Load Address: 0x48080000
Entry Point: 0x48080000
Hash algo: crc32
Hash value: bcc5d064
Hash algo: sha1
Hash value: 66756f5105d8316dc96740c4946d9feb04fcbe87
Image 1 (fdt-1)
Description: ARM64 OpenWrt BPI-R4-SD device tree blob
Created: Wed Apr 24 15:22:57 2024
Type: Flat Device Tree
Compression: uncompressed
Data Size: 35589 Bytes = 34.75 KiB = 0.03 MiB
Architecture: AArch64
Hash algo: crc32
Hash value: 9388e8a4
Hash algo: sha1
Hash value: 39e6a39f97d9258992010898f9a483e6b3e16e64
Configuration 0 (config-1)
Description: OpenWrt
Kernel: kernel-1
FDT: fdt-1
so also uploaded to my gdrive…will test tomorrow to load from my uboot
quick test was not working…
BPI-R4> setenv loadaddr 0x80000000
BPI-R4> load usb 0:2 $loadaddr openwrt-mediatek-mt7988-BPI-R4-SD-initramfs-kernel.bin
67293911 bytes read in 5576 ms (11.5 MiB/s)
BPI-R4>
BPI-R4> bootm $loadaddr
## Loading kernel from FIT Image at 80000000 ...
Using 'config-1' configuration
Trying 'kernel-1' kernel subimage
Description: ARM64 OpenWrt Linux-5.4.260
Type: Kernel Image
Compression: lzma compressed
Data Start: 0x800000e8
Data Size: 67256276 Bytes = 64.1 MiB
Architecture: AArch64
OS: Linux
Load Address: 0x48080000
Entry Point: 0x48080000
Hash algo: crc32
Hash value: bcc5d064
Hash algo: sha1
Hash value: 66756f5105d8316dc96740c4946d9feb04fcbe87
Verifying Hash Integrity ... crc32+ sha1+ OK
## Loading fdt from FIT Image at 80000000 ...
Using 'config-1' configuration
Trying 'fdt-1' fdt subimage
Description: ARM64 OpenWrt BPI-R4-SD device tree blob
Type: Flat Device Tree
Compression: uncompressed
Data Start: 0x840241f8
Data Size: 35589 Bytes = 34.8 KiB
Architecture: AArch64
Hash algo: crc32
Hash value: 9388e8a4
Hash algo: sha1
Hash value: 39e6a39f97d9258992010898f9a483e6b3e16e64
Verifying Hash Integrity ... crc32+ sha1+ OK
Booting using the fdt blob at 0x840241f8
Working FDT set to 840241f8
Uncompressing Kernel Image to 48080000
lzma compressed: uncompress error 7
Must RESET board to recover
Resetting the board...
loadaddr should be far away to be not overridden by unpacking fit… 
@dangowrt have you an idea how i can load this huge fit? or do i need to drop unrelated things (which can be dropped from attached config?) from it to make it smaller
config.buildinfo (18,4 KB) feeds.buildinfo (355 Bytes)
edit: flashed the img to card, it boots up, but i get many messages like this:
jffs2: jffs2_scan_eraseblock(): Magic bitmask 0x1985 not found at 0x27f10008: 0x3333 instead
and
mtk_soc_eth 15100000.ethernet eth2: resolve link status: system iface=0
at the end i do not land in openwrt system…it does a reboot 
(no crash or something like this)
maybe they make some kind of rootfs extension and the filesystem was not enlarged fast enough (or not remounted or created a squashfs on top)?
tried to look how the kernel file is loaded, but the default entry is pointing to mtkboardboot which seems to be own command in uboot instead of the bootm
after the reboot it looks like the system stays running…only eth2 spams console which i disabled then it was quiet…at least 3 phys are detected and seem to be up
bpi-r4_owrt-dmesg.txt (47,9 KB)
be14.txt (53,2 KB)