Compatibility of Tiagra 4700 shifter with MTB front derailleur I am aware that with the introduction of the Tiagra 4700 groupset Shimano now uses the 11-speed road cable pull ratio also for their 10-speed road systems. Therefore a  Tiagra 4700 right shifter is only compatible with Tiagra 4700 rear derailleurs and 11-speed road rear derailleurs.

Because I would like to run smaller chainrings in the front for my 2x10 setup I need to use a MTB front derailleur. Is this possible with a Tiagra 4700 left shifter or did the cable pull ratio change there as well? If not: Can I use a Sora ST-R3000 left shifter from their 9-speed road groupset instead? What are my options? Which MTB front derailleur would I have to use with which road STI shifter?
With doubles this sort of setup can usually be made to work reasonably well. There's at least one bike I know of on the market with the exact setup you describe, the 2019 Salsa Fargo Tiagra, and it does work. Putting a triple STI on a mountain front triple crank and derailleur is where it gets bad.