The first thing to check is if the Formula RXC-142 rear hub mounted by Helix accept a 11s cassette. If not, you need to change the rear hub (what means new spokes and re-lace the wheel)

Then, indeed, it depend of what you want to archive by going to 11s.

If you want to have the same wide range as on the Helix ultralight (9-34t cassette), then you definitely need another rear hub with XD-XDR body and the hub and cassette are relatively expensive (the hubsmith hub mounted by Helix is one of the cheapest, hih=ger quality hus like from Hope or Tune are more expensive).

You of course need to change the shifter and rear derailleur. There are many options for 11s shifter and rear derailleur with big price differences.