It's a lottery to make multiple peripherals work:
-disable steam inputs from steam -> wrc10 -> options
-delete all menù and game inputs for every controller shown ingame
-choose just one controller - in my case I used the wheelbase - and assign any input you want to use from that controller page, even if coming from something else, delete other controller profiles
-start a race -> works? you're good
doesn't work -> restart game, most likely some controller got some input assigned again -> repeat the previous steps for that controller, try both deleting and not deleting its (empty) profile.
Doing this used to work for me BEFORE I got an H-shifter, now I don't bother anymore because it's just too time consuming to get it to work
