Press record on Ableton, then press play on the modular, and that’s it!
-- clivevass

So when you "press play on the modular" which module are you actually pressing play on? In my set up that button is on Pamela's New Workout, which also has Clock and Run inputs which can be used to control it externally. If I wanted to control it from my computer, lacking DC-coupled outputs which as Lugia suggested is surely The Right Thing, I would just send a click track to that clock input. It would probably need some fiddling to work but people used to use the 808 rimshot to sync old analogue gear, and I can't imagine that new gear is worse!

I never do this -- Pam is always the master clock for me. You could also try it this way. Make Ableton follow the master clock from the modular, assuming your modular brain can send clock (over MIDI perhaps?).