I switched my 1st gen kickr (10 speed cassette) to a v5 recently, that came with a 11 speed cassette.
Can I let the 11 speed cassette on the kickr when I only use ERG mode with my 10 speed groupset bike and don’t switch gears ? Or will the chain be damaged ?
It seems to work fine, but I want to be sure 
Get a 1.8mm spacer and put it behind the 10 speed cassette on your new trainer.
Yep I know that, but was just wondering if it was possible to use the 11 speed cassette with my 10 speed groupset bike, without damaging it (ofcourse in erg mode without changing gears).
If you select a cog that the derailleur is nicely aligned with, there’s no issue with using 11 speed cog with a 10 speed chain/derailleur.
Otherwise you’ll get more tons more wear on the chain, cassette and jockey wheels if it’s not aligned