I flashed the latest version of "openwrt-21.02.1-ath79-generic-glinet_gl-ar750-initramfs-kernel.bin" over uboot. After a reboot, the overlay section is missing. Custom settings are not saved.
[ 0.561309] spi-nor spi0.0: w25q128 (16384 Kbytes)
[ 0.566329] 4 fixed-partitions partitions found on MTD device spi0.0
[ 0.572898] Creating 4 MTD partitions on "spi0.0":
[ 0.577866] 0x000000000000-0x000000040000 : "u-boot"
[ 0.584066] 0x000000040000-0x000000050000 : "u-boot-env"
[ 0.590537] 0x000000050000-0x000000060000 : "art"
[ 0.596401] 0x000000060000-0x000001000000 : "firmware"
[ 0.607876] 2 uimage-fw partitions found on MTD device firmware
[ 0.614034] Creating 2 MTD partitions on "firmware":
[ 0.619179] 0x000000000000-0x000000c30000 : "kernel"
[ 0.625227] 0x000000c30000-0x000000fa0000 : "rootfs"
[ 0.631306] mtd: device 5 (rootfs) set to be root filesystem
[ 0.639078] mtdsplit: no squashfs found in "rootfs"
root@OpenWrt:~# cat /proc/cpuinfo
system type : Qualcomm Atheros QCA9533 ver 2 rev 0
machine : GL.iNet GL-AR750
cpu model : MIPS 24Kc V7.4
...
root@OpenWrt:~# cat /proc/mtd
dev: size erasesize name
mtd0: 00040000 00010000 "u-boot"
mtd1: 00010000 00010000 "u-boot-env"
mtd2: 00010000 00010000 "art"
mtd3: 00fa0000 00010000 "firmware"
mtd4: 00c30000 00010000 "kernel"
mtd5: 00370000 00010000 "rootfs"
root@OpenWrt:~# mount
tmpfs on / type tmpfs (rw,relatime)
proc on /proc type proc (rw,nosuid,nodev,noexec,noatime)
sysfs on /sys type sysfs (rw,nosuid,nodev,noexec,noatime)
cgroup2 on /sys/fs/cgroup type cgroup2 (rw,nosuid,nodev,noexec,relatime,nsdelegate)
tmpfs on /tmp type tmpfs (rw,nosuid,nodev,noatime)
tmpfs on /dev type tmpfs (rw,nosuid,relatime,size=512k,mode=755)
devpts on /dev/pts type devpts (rw,nosuid,noexec,relatime,mode=600,ptmxmode=000)
debugfs on /sys/kernel/debug type debugfs (rw,noatime)
none on /sys/fs/bpf type bpf (rw,nosuid,nodev,noexec,noatime,mode=700)
mountd(pid7303) on /tmp/run/blockd type autofs (rw,relatime,fd=7,pgrp=1,timeout=30,minproto=5,maxproto=5,indirect)
root@OpenWrt:~# df -T
Filesystem Type 1K-blocks Used Available Use% Mounted on
tmpfs tmpfs 61704 13720 47984 22% /
tmpfs tmpfs 61704 1108 60596 2% /tmp
tmpfs tmpfs 512 0 512 0% /dev
root@OpenWrt:~# df -h
Filesystem Size Used Available Use% Mounted on
tmpfs 60.3M 13.4M 46.9M 22% /
tmpfs 60.3M 1.1M 59.2M 2% /tmp
tmpfs 512.0K 0 512.0K 0% /dev