I put all circuits in post #7.
Oscillogram with and without spikes is in #4 post.
All others oscillograms looked similar, that's why i wrote it works or not.
I try to be careful. I have already seen:
I would like to go back to this circuit:

If there is only a resistor without a capacitor, how is the RC filter formed here?
I know that the probe has some capacity but very small.
With 1k resistor spikes appearing. With 10k or more all looks good. Why?