I use insert effects and now I have the following problem:
Is it posible to set the effect strength?

It depends on the Effect Type you select.
Among the Insertion Effects are various types of processors, those that are effects in the common use of the term, and those that are more “utilities” than they are Effects.

For example, an Insertion Effect Type that is a Reverb, or a Time Delay will likely have a “Dry/Wet” Balance to allow setting *how much* data travels through the processor and *how much* remains dry (normal). This is always a subjective determination... set to taste.

However, the Insertion Effect Types that are utilities, there will be no subjective determination. For example, an Equalizer. You always send 100% of the signal through the EQ. There is no benefit to sending only part of the signal through an equalizer, in fact, that would be detrimental to the phase of the resulting signal. So utilities like EQs, Compressor/Limiters, Rotary Speaker, some of the Speaker emulations... there is no Dry Wet Balance because the way the processor Type does what it does eliminates the need for a Dry/Wet Balance.

This is not a hard and strict rule. Whether or not there is a Dry/Wet Balance depends on the Effect Type you’ve selected. For example, the Wah models are truly Effects (more than they are utilities) but there is no Dry/Wet Function on the real thing either... all the signal goes through the wah filter... same as it would on a guitarist’s wah-wah pedal.