I am pretty sure you need to configure more (fake) buttons for the handbrake, I had the same problem. Otherwise it does not get recognized as a gaming device.
I can look up later how I solved this or you can ask the simracing linux community, which helped me with a couple of similar pronlems before:
A place for all the niche of niche gamers to discuss and join other simracers!
Join the Simracing space here https://matrix.to/#/#simracing:matrix.org
I am glad to hear you got it to work! I think I took notes on how I got it to work. But I remember having also added a similar rule as you did at some point. I may be able to find my notes tomorrow.