”So do I understand you right that you need a kind of LFO that goes very slowly up to a certain maximum value and then holds that value, right? How long should that hold that maximum value?
-- GarfieldModular”

Exactly!
I want it to hold the value until it get a new trigger/gate and starts over again from one level to another.
I guess it requires a complex patching or maybe it is not possible?
Maybe some kind of LFO but I rather think of some other kind of function generator like Maths or an advanced EG.
One patch I will test:
Three oscillators are tuned to the same pitch e.g. C1.
Osc 1 then slowly raise to C2. Osc 2 to E2 and Osc 3 to G2 (with different speeds) so a chord is evolving from the C1 pitch.