Migration from PandoraBox to OpenWrt on Xiaomi Mi WiFi Mini

I have the same situation, as was discussed and this topic, where it was suggested to use the web-interface of Pandora to flash an OpenWrt firmware:

The topic is marked as Solved and, as far as I understood from it: the author just flashed OpenWrt from Pandora web-interface or not ?

I've tried to flash the openwrt-21.02.2-ramips-mt7620-xiaomi_miwifi-mini-squashfs-sysupgrade via Pandora web-interface, but what I get is:
"The uploaded image file does not contain a supported format. Make sure that you choose the generic image format for your platform."

What do I do wrongly, please ?
My Pandora version currently is this one:

Perhaps, it's required to downgrade Pandora to an older version to be able to flash OpenWrt via web-interface, please ?

Thanks in advance.