Ping fluctuations on laptop?

I have had very strong ping fluctuations on my computer for a week. Often the ping is between 20 and 40, until it jumps to over 500 for half an hour or more and stays there. The problem mainly occurs on my computer. I have already restarted the router, I do not have a LAN cable.

What could be the reason and what could I do about it, if it really is my computer?

Either the network settings or poor reception conditions or fluctuations caused by the provider. I would rule out a defect in the router. A LAN cable is not expensive, and many can borrow a surplus of them. That would be the next thing to try out whether stable conditions are possible with it.