If you have this firmware, your TP-Link TL-WR850N is functioning as intended at the time of its last official support window (April 2021). It is time to consider upgrading to a Wi-Fi 5 (AC) or Wi-Fi 6 (AX) router if you need modern security, but as a legacy device, Build 210407 is the best you will ever get.
Connect to the router and go to http://tplinkwifi.net or 192.168.0.1 in your browser. 3.16.0 0.9.1 v6031.0 Build 210407 Rel.7370n -TL-WR850N-
If you are trying to update to a newer version or restore this version: If you have this firmware, your TP-Link TL-WR850N
The TL-WR850N is a wireless router that supports: If you have this firmware