Opkg problem with custom build

I've decide to build my own build of openwrt since I discover that my kuwfi AP has a customized version of openwrt (https://breed.hackpascal.net/, I think). The problem with vanill pre-built version was that wifi isn't supported, while the device is an access point.
So I've explored a bit the "make menuconfig", then fix what I broke in previous step, then installed feeds need as per error given by "make".
The big problem of my custom openwrt is that opkg do not work: no error message but no message at all, the best I get from it is
opkg -v 4 opkg version d038e5b6d155784575f62a66a8bb7e874173e92e (2022-02-24)
No available pkgs, no output when passing update arguments, ...

Any suggestion to fix this?

they all have.

that's a boot loader ...

I assume it isn't the KuWfi T-MB5EU ?

The device has cpu mt7621, can't find model. The bootloader is readonly?

That's extremely vague...

At Openwrt, or Kuwfi ?

They usually don't get replaced/updated, if that's what you're referring to.

On kuwfi I found a product somewhat similar that is AP930. On the back I have:
model: 7621A106
High performance 11ax 1800Mbps Wireless AP.

I've decide to build my own firmware since can't install wifi firmware/util using opkg on vanilla openwrt pre-built firmware due to lack of mem

Mem, as in flash ?

The flash has 100Mb free, the overlay partition(?) has only 160Kb free

seems like opkg isn't properly installed: missing /etc/opkg/distfeeds.conf

Note that you packages compiled with similar compile options, kernel versions etc.
In practice, you likely need to download from your device's OEM's repo, not from the general OpenWrt as the packages in some our ancient branch will not be fully compatible with the OEM hacked version of OpenWrt.

if I create the file with

src/gz openwrt_core  http://downloads.openwrt.org/snapshots/targets/ramips/mt7621/packages
src/gz openwrt_base http://downloads.openwrt.org/snapshots/packages/mipsel_24kc/base

at least opkg update works! As hint everything went ok in building vanilla openwrt.
Now have to figure out if can bring up wifi.