I tried with Cakewalk Sonar, and even though I have no idea what I'm doing in that thing, it looks like everything works. Detected Helix right away, recording on 1-2 records wet, on 7-8 dry, opens Helix ASIO settings...
I wrote "upgraded" to W11, but I didn't actually upgrade from 10, it was format C: kinda thing, everything is brand new. But it's obviously a Reaper thing, not Windows or Helix thing.
I'll switch to Reaper forum.
Thank you for your help!