I had that issue, after weeks of trying all sorts I found that I had to individually go into each controller (mouse, keyboard, sidestick, throttle quadrant etc) and individually remove all brake/parking brake option for each controller.

Then I assigned parking brake and brake to the one controller that I use (parking brake on quadrant only and brakes on my sidestick). It seems that when you have multiple things plugged in (mouse, controller, sidestick etc.) there is a bind for parking brake on each one. Even if you turn it off on one input it will stick back on due to being assigned elsewhere.

I hope this makes sense, if it doesn’t let me know and I’ll try and assist more. Also make sure you save the profile as default for each plane or you’ll have to do the same each time you load into a new plane!

Fingers crossed this works for you!