I am able to successfully deploy openwrt 24.10 on TP-Link Archer C20(IN) V6.8. All ports , radios , mac ,buttons & leds working fine.
Step 1 : Grab router's stock firmware.
but as of now stock firmware for this router is not listed on tplink website, so I dumped the firmware by desoldering the xmc 8MB flash & hooking it into my programmer.
You can ask tplink for the firmware of this router.
Step 2: Download the C20 v5 Openwrt.bin file.
Step :3 you have to replace the kernal+rootfs in stock_firmware.bin with openwrt.bin (kernal+rootfs) .
I. In stock firmware image kernal+rootfs starts at 0x50000 & ends at 0x7C0000. It means if we convert the hex to decimals then the size will be 7.4 MB (kernal+rootfs).
ii. So first we have to make openwrt sysupgrade exactly 7.4MB. for this we have to add paddings in the binary file.
truncate -s 7798784 openwrt.bin
iii. The above command will make the openwrt.bin of exactly 7.4MB of size.
Iv. Now inject this openwrt.bin into stock_firmware.bin at exact location i.e Start address 0x50000 to end address 0x7C0000.
Leave the last 256KB of flash untouched that's from 0x7C0000 to 0x800000
dd if=openwrt.bin of=stock_firmware.bin bs=1 seek=$((0x50000)) conv=notrunc
now you have a file "stock_firmware.bin "having openwrt(kernal+rootfs).
STEP 4: Load modified Stock_firmware.bin in tftp server & flash it into your router by powering on holding reset button.
Congrats , you have openwrt running on your TP Link router C20 (IN) v6.8.
STEP5 : initially 5GHZ chip (mt7613ben) will not work , you have to add packages
kmod-mt7615e
kmod-mt7663-firmware-ap to get it fixed.
HAPPY MODDING 
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I'll raise a PR let's see whether it will get accepted in supported devices or not.