11s cassette compatibility with 12s DI2 group set

Hi there!

I am thinking about getting a new road bike with a 12s group-set (Shimano 105 Di2 R7100, 12s).

On my trainer, I have a 11s 11-34t 105 cassette that works great not only with my road bike but also my girlfriend’s 11s Ultegra equipped bike.

Any experience with 11s - 12s compatibility? It would be great if we both could keep on using my trainer and I don’t have to keep my old road bike.
Google gives me mixed answers…

Thanks everyone!

I saw 11speed cassette with 12 speed sram AXS https://www.youtube.com/watch?v=DBQFZ8f4Hgo
And look at these topics:
12 speed groupset on an 11 speed cassette on the turbo - #3 by mikethewhite
Reddit - Dive into anything

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Thanks for your answer! Probably the chain and the cassette will wear down a bit quicker, but I think I can live with that. Better than the alternative of getting a second cassette or trainer or even to keep my old road bike.

Good Easter weekend to you from Germany!

I run 12 speed (sram axs) with 11 speed shimano casette on the trainer and runs fine albeit i dont change gears too much as erg mode used most the time.