Compared to the web version of ThinLinc, the native ThinLinc Client have several advantage:

Copy/Paste work seamlessly between seedbox desktop and your local computer. There's no need to use clipboard box as you would when using web version.

ThinLinc Desktop Client runs natively on your computer instead of relying on browser's JavaScript implementaion.

You can easily resume, end or even create new desktop session. The web version may or may not be able to resume previous session if the connection was abruptly ended.

Cendio provides Thinlinc Desktop Client on this page :
​https://www.cendio.com/thinlinc/download/
​
It support all major operating systems. Just pick the one for your operating system and run it to install.

The ThinLinc client allows you to easily specify a different SSH port through its configuration options. The following steps apply to the native ThinLinc client application (available for Windows, Linux, and macOS):

Start the ThinLinc client application on your local machine.

Before attempting to connect, you need to open the client's configuration options:

In the main client window, look for an "Options..." or "Settings" button.

Clicking this will open a configuration dialog with several tabs.

Inside the options dialog, locate and click the "Security" tab (or a similar section related to connection security or advanced settings).

Within the "Security" tab, you will find an option labeled "SSH Port" or something similar, which allows you to specify the TCP/IP port for the SSH connection.

The default value will likely be 22.

Change this value to 2222.

In the main ThinLinc client window, enter the Server address (hostname or IP address) of your ThinLinc server.

Enter your Username (by default it is just user )and Password (or use the appropriate authentication method).

And click "Connect". In case you have previously connected before. it will present a choice where you can end, reconnect or create new session