GRX doesn't work with Shimano MTB pull ratios AFAIK?
Also you can get a Sunrace 12 speed cassette that fits on a standard 11s freehub no bother. Not all 11/12s cassettes will fit on 10s freehubs though.
Technically, I don't think 105 will either, but it can be made to work
https://bikepacking.com/gear/guide-to-mullet-drivetrains/
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GRX doesn't work with Shimano MTB pull ratios AFAIK?
Also you can get a Sunrace 12 speed cassette that fits on a standard 11s freehub no bother. Not all 11/12s cassettes will fit on 10s freehubs though.