Moza Multi-function Stalks not working with Flatpak Steam

**Game information**
Any game using Proton but I have tried Euro Truck Simulator 2, Wreckfest 2 and Dirt Rally 1

**Distribution name and version where applicable**
Arch Linux

**Flatpak info**
Flatpak 1.16.1
flatpak --gl-drivers:
default
host

**Problem description**
The stalks work using Boxflat: https://github.com/Lawstorant/boxflat. This is installed using Flatpak. This program using a udev rule to create an input called Boxflat multifunction stalks:

This works perfect in KDE Game Controller tester and shown above but when opening Flatpak Steam and using Proton no games detect it as an input. Furthermore, it doesn't show under Settings > Controller either in Steam. When using Native Steam it shows up under Settings > Controllers and in games and works perfectly so this is definitely an issue with flatpak steam. When trying Native Linux games it shows up as an input.

Steam and Boxflat both have device=all permissions under Flatpak. If logs are needed please let me know which ones are required. I couldn't find anything related to devices in the Proton or Flatpak run logs but I'm more than willing to send them over.

**Does this issue reproduce with native Steam**
No the Moza Multi-function Stalks work perfectly with Native Steam