Doepfer

The only Eurorack module I know until now is the Analog Solutions RS-35,
which is out of production unfortunately.

Expert Sleepers Disting has a pitch and envelope tracker setting which is basic but quite effective (and you get 15 other functions included). As with all pitch trackers, the quality of what comes out of it is very dependent on the quality of the signal going in. To get dependable tracking you need clean consistent audio with a limited spectral range beyond the fundamental frequency. The Disting tracker doesnt incorporate anything to help with that. So you will need to experiment with compressors, gates and bandpass filters in the pre-tracker audio chain to get consistent results.

If you want a consistent and reliable way to have conventional melodic control over a synth from a guitar, I think its much simpler to do it via midi. Tracking audio pitch to CV will often give up really interesting outcomes. Its a great way to generate happy accidents. But if you want an equivalent of the certainty of keyboard control its not going to work for you.