Can you combine RAM with different capacities (4GB + 8GB)?

With two slots in the notebook, 4GB RAM can be expanded by 8GB

You can. But would not be advisable. It would always be better to use two identical bars.

Yes… The clock frequency is important, it should be the same

Yes you can. However, the specifications must be the same. However, the question arises whether you still have a free slot. Otherwise you would have to buy two - 4GB each per slot. So that the RAM are of the same series, Mhz / Ghz. I would recommend either way.

Thank you, can you expect a loss of performance or is there a generally greater risk?

Is not a problem in the notebook, but both memory modules should be of the same type, even if the size is different!

It doesn't even have to be from the same manufacturer, but the clock timers should be identical if possible, otherwise one of the modules will cause crashes or slow down the computer!

Thank you, I have two slots, the 4GB is in one - I have now bought an 8GB bar. Now I could add it - or just the 8GB…

Better then just insert the 8 GB. I would put the 4 in a plastic bag or in its 8GB packaging and store it. Should the 8 GB say goodbye, you still have the opportunity to fall back on the 4 GB.
For the following reason, that the two RAM have different voltage, clocking, frequencies etc., this could become a disruptive factor that drives your laptop to the edge of madness. (figuratively speaking).

Oh yes, avoid using your hands to touch the contacts or the surface of the RAM. Actually, you should buy antistatic gloves if you install something like this. This avoids possible charging of the part and grease deposits, which could lead to a fire.

Thank you

Thank you