Extremely slow wifi with elitebook 820 g3

[Thomas53600]

Hello, I installed bigsur on my hp elitebook 820 g3, but the wifi is extremely slow. When I do a speedtest, I get correct values (100 mb/s sending, 80 receiving) but when I go on the internet, the page loading time is very long. Also, the app store takes at least a good 20 seconds to display images related to products, and downloads from the app store go at an average speed of 0.1 mb/s every 10 seconds, which is just unusable. My network card is the basic built-in one, an AC-8260. i tried with kext airportitlwm as well as with itlwm + heliport. could someone help me? Thanks
Im joigning my EFI.