Wi-Fi speed low

this could be a result of not updating the software. try and reinstall the drivers for the internet.

that may solve your problem, if not it most likely means you have a weak internet signal where the thinkcentre is positioned.

you may just need to restart your router or possibly get a new one.

Disclaimer: Please note that the following consists of information I had aggregated when looking into Think Centres recently. It is in part conjecture on my end. I have no first hand experience with the parts I suspect to be the issue and opted for another vendor when ordering my Think Centre.

This might be due to a Realtek WiFi module M.2 add-in card. Some of them are infamously troubled, with people having to reboot their system or having to even reinstall the driver periodically in order to reset the card. Sometimes OEMs update the drivers and fix issues, only for them to reappear days or hours later (I suspect, it is due the driver update performing a reset instead of actually fixing the issue). So, if the issue is fixed by simply reinstalling the driver (or updating it), but then it reappears, you might have one of the affected models installed in your machine. Some users report that modules by other vendors e.g. Intel fixed the issue for them.

Other suggestions still apply. The recommendation is to do any testing right next the the access point. It doesn't have to be at touching distance, but close enough to guarantee there are no sources of interference, nothing is blocking and signal attenuation is at a minimum.

PS: Somewhat amusingly, Intel seems to have the reverse situation of Realtek: reliable WiFi and broken LAN. I have first hand experience with the LAN part.