You can use the following command to open a defined URL using the systems default browser via the command line:
cmd "start /max http://url.com"
Please note, that in order to use this command, you will have to config the external application as follows:
Command = C:\Windows\System32\cmd.exe
Argument = /c "start /max http://url.com"
Thanks for that solution! Wanted to add a OneNote Link in there for easy access to solutions when connecting to a server.
Tho I may have a bit of an improvement as the above threw an error for me. It's better to use the following argument instead to also handle special characters in the URL:
/c "start "" "google.at""
Additional to that it's advised to go to Advanced Options and enable "Start Unattached" to not unnecessarily open a new tab inside Royal TS.