Quick update so as to not lead anyone who might find this thread later to believe that Freeplane doesn’t work on an X230 with Qubes:
I found the error that I made, and it works fine now.
If you are planning to use Freeplane on Qubes, whether on an X230 or newer hardware, it should run fine. To see some of the mistakes that I made at first regarding this, as well as very helpful instructions that I have received from others about this, you can have a look at this thread:
But this is probably only relevant for you if you are planning to use Freeplane on Qubes, and / or if you have any difficulties with doing that.
Happy Qubing!