The problem here is that none of the default fonts have the full font set, nor are Unicode compliant.
However, on UIFlow 1.13, and in my case the Fire board, I have a font "Unicode 24". This one actually supports the pound symbol just fine.
0_1714585176841_Screenshot 2024-05-01 at 19.38.39.png
I suggest best if you are trying to make a UI to import a separate PNG for the GBP symbol and place it where needed.
Cheers