But I don't know if the price makes sense. Better to sell the SLX derailleur and buy a GRX one in my opinion. Less of a hack and cost wise maybe not even a difference.
You have committed a thought crime. Do not attempt to escape. The gravel police are on their way to apprehend you, whereupon you will be ritually decapitated with a 33mm tyre spinning at high speed (they cut through much better than a 2.1")
Because you already have the SLX derailleur?
There are pulleys that convert the cable pull. E.g. Wolftooth Tanpan:
https://www.bike-components.de/en/Wolf-Tooth-Components/Tanpan-Shimano-11-speed-Inline-Drivetrain-Converter-p64107/
But I don't know if the price makes sense. Better to sell the SLX derailleur and buy a GRX one in my opinion. Less of a hack and cost wise maybe not even a difference.