That detail changes the diagnosis,
@Bjorn Ivar. Backpedalling on any hub will spin the cassette regardless of health - the freehub is designed to disengage in reverse, so cogset movement there doesn't confirm anything's working.
But combined with "rear wheel doesn't move" when you pedal forward, this now points away from the sensor/motor and towards the freehub itself. If forward pedalling drives the chain and cassette but the hub shell still isn't turning, the pawls or ratchet mechanism inside the freehub aren't catching - a straightforward mechanical failure, not a Shimano STEPS fault at all.
The decisive check: lift the rear wheel off the ground and turn the pedals forward slowly. Watch the wheel itself, not the cassette.
• Wheel spins immediately, tracking the pedal input = freehub's fine, and we're back to looking at the motor/sensor side.
• Cassette and chain turn but the wheel lags or doesn't move at all = freehub's not engaging. Worn or gummed-up pawls, snapped ratchet ring, or a freehub body that's given up.
If it's the freehub, the good news is that's a wheel/hub job rather than internal motor work - a freehub body swap is common and nowhere near as fraught as opening up a drive unit. The W292 code may simply be honest: if the wheel genuinely wasn't turning, the system would correctly report no speed signal, sensor and magnet innocent all along.