@Virgo
Thanks for your suggestions.
Firefox does work, the ER605 on Firmware 2.1.2 signs on and is useable as before.
It was a surprise to me when a Brave Private Window also worked normally! Was there some logic behind that suggestion or just random option?
I cleaned the cache but a normal Brave window is still rejected with "Unsupported Browser"
I suspect something in the TP-Link code is not being handled correctly rather than a specific choice by TP-Link to stop support for Brave, especially as a Private Window works!
This finding would suggest a difference between the default settings for normal and Private windows may be causing a problem, any ideas as to what?
Thanks again