Can you please post /tmp/.x2go-<user/.../session.log?
Here it is:
Running as X2Go Agent
NXAGENT - Version 3.5.99.23
Session: Resuming session at 'Wed Jun 23 17:47:10 2021'. Info: Proxy running in client mode with pid '97958'. Info: Using errors file '/tmp/.x2go-stefan/C-stefan-50-1624442948_stDXFCE_dp24/session.log'. Info: Using stats file '/tmp/.x2go-stefan/C-stefan-50-1624442948_stDXFCE_dp24/C-stefan-50-1624442948_stDXFCE_dp24/stats'. Loop: WARNING! Unrecognized session type 'unix-kde-depth_24'. Assuming agent session. Warning: Unrecognized session type 'unix-kde-depth_24'. Assuming agent session. Info: Waiting for connection from 'localhost' on socket 'tcp:*:52199'. Info: Accepted connection from '127.0.0.1'. Info: Connection with remote proxy completed. Info: Using ADSL link parameters 1408/24/1/0. Info: Using agent parameters 5000/10/50/0/0. Info: Using cache parameters 4/4096KB/8192KB/8192KB. Info: Using pack method '16m-jpeg-9' with session 'unix-kde-depth_24'. Info: Using ZLIB data compression 1/1/32. Info: Using ZLIB stream compression 4/4. Info: Using cache file '/tmp/.x2go-stefan/C-stefan-50-1624442948_stDXFCE_dp24/cache-unix-kde-depth_24/C-C8625BFEF4F19E8C76E6C9540816BD14'. Info: Listening to X11 connections on display ':50'. Info: Established X client connection. Info: Using shared memory parameters 1/1/0/0K. Info: Not using local device configuration changes. Info: keyboard blocking directory created: '/home/stefan/.x2go/C-stefan-50-1624442948_stDXFCE_dp24/keyboard' Info: Keycode conversion is off Info: re-reading keystrokes configuration Warning: Cannot read keystroke file '/home/stefan/.x2go/config/keystrokes.cfg'. Info: using keystrokes file '/etc/x2go/keystrokes.cfg' Info: ignoring unknown keystroke action 'debug_tree'. Info: ignoring unknown keystroke action 'regions_on_screen'. Info: ignoring unknown keystroke action 'test_input'. Info: ignoring unknown keystroke action 'deactivate_input_devices_grab'. Currently known keystrokes: close_session Ctrl+Alt+t switch_all_screens Ctrl+Alt+f minimize Ctrl+Alt+m resize Ctrl+Alt+r defer Ctrl+Alt+e ignore Ctrl+Alt+BackSpace force_synchronization Ctrl+Alt+j fullscreen Ctrl+Shift+Alt+f viewport_move_left Ctrl+Shift+Alt+Left viewport_move_up Ctrl+Alt+Up viewport_move_right Ctrl+Alt+Right viewport_move_down Ctrl+Alt+Down Session: Session resumed at 'Wed Jun 23 17:47:15 2021'. Info: Screen [0] resized to geometry [1024x768] fullscreen [0].
You should ensure setxkbmap -query will output the same both on the client and inside the session. If that is not the case we need to find out why that is.
it is the same on both systems:
rules: evdev model: pc105 layout: de variant: nodeadkeys
As you have "xfree86" in your output I think xfce fiddles with the keyboard settings. This leads to the question if it works if just start an xterm instead of a full blown desktop.
If I only start xterm, I get the bracket und the arrow key works as expected.
Thanks for helping me,
Stefan