Ahoj,
the UniGraphic library is little bit old and during last 5 years were too much changes in the MbedOS and also its tools and the library is not maintained by owner or community via PullRequests. Usually, when you check the Forks, you can find a copy of original repository which is not so old and that can work.
Here you can see a version of UniGraphic by Duncan McIntyre . That looks like already fixed.
If you want to fix it by yourself you need to follow compiler messages and fix all erros.
- In the folder of the library you can find folder with name
Fontand all files inside include line with__align(2). You need to commented it out//__align(2). - in the
TextDisplay.hyou need to add#include "Stream.h" - and so on.
BR, Jan