I’m sorry for the late reply.
S1300 is EMMC parition firmware by default.But ‘EMMC partition firmware’ is not currently supported on openwrt-21.02.0.So you need to switch ‘EMMC partition’ to ‘nor partition’.
First,you need update ‘s1300-openwrt-to-factory.img’.please refer ‘GitHub - gl-inet/openwrt: This repository is fork from openwrt official repo, we will update the latest tag and release GL.iNet firmware based on it.’ and download ‘s1300-openwrt-to-factory.img’.
Then, You could upgrade the firmware compiled by openwrt-21.02.0 normally.