I installed the new 64bit Client (1.0.0) on my Ubuntu 20.8 (buster) system, with Firefox, and Playonlinux(Wine) as described in the german Forum. created a TSO_Client.desktop file (also discovered in the german forum), and inserted an entry in the mimeinfo.cache file. I copied the client.swf wich was in the Windows-TSO Directory after succsessful connection to the testserver in to the installation-Path of the Playonlinux-TSO eg
~/.Playonlinux/wineprefix/default/drive_c/users/<username>/Local\ Settings/Application\ Data/Ubisoft/The\ Settlers\ Online/Client.
Now the client start properly, connected to the testserver, and if the game are loaded, the client freezes.