fwiw, did you use the modified firmware by @adrianschmutzler ?
https://forum.openwrt.org/t/help-in-unbricking-tp-link-archer-c60-v3/62642/21
If you read the thread, there is a known problem with version numbering which prevents any attempt to reload stock firmware.
The modded firmware appears to be based on original firmware version Archer C60(EU)_V3_190115.
https://www.tp-link.com/de/support/download/archer-c60/#Firmware
File sizes are the same, except for the header and checksum which have been modified.
Use the modded file at your own risk of course.