A web site I want to use refuses to operate because it says I am using Opera and it wants me to use Chrome, Edge or Firefox. I tried setting the Browser Id, in settings to 'Desktop', but that made no difference. On the desktop I can use Opera with no problems on the same site so I can't see that when I switch to 'Desktop Option', on Android Opera, that it is the same as my desktop Opera.

So, in summary, I want to change the User-Agent to my own custom value. How can I do that please since about:config etc. no longer works?