When Shimano finally released the Di2 12speed GRX, a proper 1x variant was missing. That doesn't mean we can make our own solutions.
This time I wanted 1x with either 42 or 44 in the front with Shimano's XT 1045 in the back, almost a 10 tooth "out of spec" cassette. But it does kind of work!

Mentioned parts: (links for convenience, no affiliation!)
Shimano RDRX825 Rear derailleur:
https://r2bike.com/SHIMANOGRXDi2R...

Wolftooth Roadlink DM:
https://www.wolftoothcomponents.com/p...

Shimano service documents for part number referencing:
https://si.shimano.com/en/


Chapters:
0:00 Introduction
1:22 1x GRX 12speed what works
5:33 Outside testing
11:38 Offset cage modification experiments (failed)
13:33 Breaking the derailleur
16:13 Relaaaax 2x still works fine....