MacBook Air 2015 is very slow when Wi-Fi is activated since macOS Monterey 12.7.6 update

That looks reasonable when using a 2.4Ghz connection, so it is not a loose antenna. It could still be a hardware issue with the wireless card or even the Logic Board.

Since you do have about 90GB of Free (aka Libre)storage space, you can create a new APFS volume and install macOS onto the new APFS volume in order to test out a clean installation of macOS. There is no need to install any apps, or to restore/migrate from a backup since you want to test a clean OS (plus you don't have enough room for more than just the barebones 2nd OS). If you have the same issue with this bare bones clean install of macOS to the new APFS volume, then either the APFS file system has a problem, or you have confirmed a hardware issue of some sort with the laptop. Once you are done testing you should delete that new APFS test volume since you will be running borderline on not having enough Free storage space.....bad things happen if you completely run out of Free storage space. Ignore the "Available" storage value (aka Disponsible) since it is very misleading at least in English.

MQKING wrote:

I installed CleanMymac because of this issue, i thought it will resolve , i uninstalled it long time ago after two scans finding no problems.

Unfortunately one of the problems people have with CMM is uninstalling it completely even when you use the CMM uninstaller. The EtreCheck report clearly shows CMM is still partially installed on your system & likely causing problems.

Daemons launchd: 
  [Engagé] com.macpaw.CleanMyMac5.Agent.plist (Pas signé - installé 2025-04-15)
    Exécutable: /Library/PrivilegedHelperTools/com.macpaw.CleanMyMac5.Agent

You can try booting into Safe Mode and trying to manually delete the file(s) which should be located at:

/Library/LaunchDaemons/com.macpaw.CleanMyMac5.Agent.plist

/Library/PrivilegedHelperTools/com.macpaw.CleanMyMac5.Agent

If you there are any more files/folders anywhere on the Mac for "macpaw", or "CleanMyMac", then delete those items as well. You will need to log into an admin user account in order to delete the files I listed>

I also don't know what HoRNDIS is, but it may be the source of your Mac's performance issues. Uninstall it by following the developer's instructions.

Try running Disk Utility First Aid on the hidden Container. Within Disk Utility you may need to click "View" and select "Show All Devices" before the hidden Container appears on the left pane of Disk Utility. Even if First Aid says everything is "Ok", click "Show Details" and scroll back through the report to see if any unfixed errors are listed. If errors are listed, then run First Aid again until the errors are gone. If after several scans the errors remain, then you will need to run First Aid while booted into Recovery Mode.

Also make sure to disconnect all external devices in case one of them is causing a problem.

Try running the Apple Diagnostics to see if any hardware issues are detected.

Edit: Plus I see Security Integrity Protection (aka SIP) has been disabled. Which app required this? It is better to avoid an app which requires you to compromise system security or find another app to use instead.

Uninstall CleanMyMac since it is notorious for causing all sorts of problems. Anti-virus apps, cleaning/optimizer apps, and third party security software are not needed on a Mac since they all usually cause more problems than they solve because they interfere with the normal operation of macOS at a low level.

MQKING wrote:

The OS ran already smoothly when the wifi is OFF

But It is still slow when wifi is ON.

Maybe a hardware issue with the Airport card?

That's what I'm thinking.

Or it is possible the WiFi antennas have come loose a bit. Just curious what the WiFi connection information is.....you can get this by Option-clicking the WiFi icon on the menubar. Important items are Channel, RSSI, Noise, Tx Rate, PHY Mode.

Run the third party app EtreCheck and post the complete report here so we can examine it for possible clues.

How to use the Add Text Feature When Posting an EtreCheck Report - Apple Community