I2C Master and Multiple slave configuration: How to cut off capacitance of unused I2C devices
I can't imagine that a device/chip will have an input capacitance any greater than typically 10 pF so, the majority of the capacitance of the system will arise due to the cabling. You can approximately say that cable has 100 pF of capacitance per metre and so 2 metres of interconnecting cable will roughly be 200 pF.

Is there a chance that I do a sort of multiplexing and cut off the
capacitances of the unused slave devices?

If you are that close to your system having problems with too much capacitance, you should try a different approach. 5 devices of (max) 20 pF each is only 100 pF. The cable will be about 200 pF and, the generally accepted capacitance limit for I2C is 400 pF. You should be OK without multiplexers.