Vlad
Ok, put custom UA in Orion Preferences - Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Firefox/91.0
web sites are expected to detect my browser as FF 91 and it is used on Linux OS. For many websites this is true
But if web-sites uses advanced detection it detects the operating system as MacIntel and its very bad for security and anonymity reasons. So now valid UA for use with Orion should always contain MacIntel etc. but never Linux or Windows.