Thank you to answer so fast
I use free Avast in Windows 10 Pro (so with Windows Defender too) and from the beginning I use Avast.
I discovered this problem when I got a fibre connexion, before it was too slow to be notable, now Avast uses all the power of the CPU and tortures my computer.
The first link you send me can be a solution, but I suppose it will impacts the others Avast processes, is there a way to only deactivate the web agent for specific applications?
And I don't understand the purpose of your second link
Anyway thank you again for helping me