Tp-link archer c6 have 8mb of storage but LuCI Shows it have 1.31mb of storage
Device: Tp-link Archer C6(EU)
OpenWrt Version: 22.03.2 r19803-9a599fee93
Luci: openwrt-22.03 branch git-22.288.45147-96ec0cd
I would guess that is because the bulk of the available storage is used to store read only filesystems, and only ~1.31 MB are available for the overlay. Not knowing details of your device this is just a guess though.
By default installation it had many packages installed that's why it shows your storage is 1mb you can run
df -h in your openwrt terminal to see your actual storage specifications including disk and temp storage...
You need a pendrive via usb as storage: