See the attached screenshot. It's the same in all three Affinity apps, on a 2018 Mac mini with Big Sur 11.2.1 and a 4K display (4096 x 2304; in the System Preferences the resolution is set to "Default for display").
On an older 15" MacBook Pro with macOS Catalina 10.15.7, that panel looks fine, the text isn't truncated.
The Affinity apps are all v 1.9.1, but I've noticed this issue on 1.9 as well.