I recently bought a t500rs and a th8a shifter. I set it all up, installed all the latest drivers and started lfs. I went to the settings just to see that I only could use one of the devices at a time since lfs sees them as different devices. Anyone know what I can do?

Dunno but I think u connect that to trustmaster wheel and set gear shift mode to shifter in LFS?

I see th8a shifter has usb and is new device.

Have no qlue sorry

Isn't there a checkbox/option whether you want devices separated, or joined together (on the controls screen)? I tried myself, but I don't have any device connected, so I don't see anything like that.

multiple devices work for me:
I use G27 wheel and an usb-buttons-thing, both can be used together in LFS.

If you go to options->controls and hold down buttons on wheel/shifter, do the pressed controls get displayed?

There is a single controller mode and a multiple controller mode.

See the attached images.