LENOVO PC very slow

No infection on your PC, just a few outdated processes; there isn't much to do since you have a very low-powered processor and you only have 3.5 GB of RAM available, which is the reason for your PC's slowness.

You have installed Avast; it slows down your Windows 10 PC because its built-in antivirus is sufficient and effective, activating automatically when no other antivirus is installed, so uninstall Avast using [https://www.avast.com/fr-fr/uninstall-utility#pc this Avast utility) your PC should be a bit faster without Avast, which I consider unnecessary.

To remove outdated processes:
Procedure to follow in the indicated order:

1- Open FRST as an administrator; for this, right-click on FRST and choose run as administrator
2 - Copy the entire script in the box below:

Start::
CreateRestorePoint:
CloseProcesses:
Task: {40156590-6F78-4D06-805F-A0B55E1D56F9} - System32\Tasks\Avast Software\Overseer => C:\Program Files\Common Files\Avast Software\Overseer\overseer.exe /from_scheduler:1 (No file)
Task: {CCDFC0B8-01A3-4E74-A820-4F13F51D269E} - System32\Tasks\Microsoft\Windows\Mobile Broadband Accounts\MNO Metadata Parser => C:\WINDOWS\System32\MbaeParserTask.exe (No file)
Task: {DAED4FB3-C0AF-46C6-A1E6-4ECA80478934} - System32\Tasks\Lenovo\Vantage\Schedule\VantageTelemetryAddinTask => C:\Program Files (x86)\Lenovo\VantageService\3.6.15.0\ScheduleEventAction.exe VantageTelemetryAddinTask (No file)
Task: {e780fd3b-fbd1-43df-a331-c1c50de351b4} - no file path
S1 WinSetupMon; system32\DRIVERS\WinSetupMon.sys [X]
HKLM\SOFTWARE\Policies\Mozilla\Firefox: Restriction 
ShellIconOverlayIdentifiers: [00asw] -> {472083B0-C522-11CF-8763-00608CC02F24} => C:\Program Files\Avast Software\Avast\ashShell.dll -> No file
ShellIconOverlayIdentifiers-x32: [00asw] -> {472083B0-C522-11CF-8763-00608CC02F24} => C:\Program Files\Avast Software\Avast\ashShell.dll -> No file
ContextMenuHandlers1: [avast] -> {472083B0-C522-11CF-8763-00608CC02F24} => C:\Program Files\Avast Software\Avast\ashShell.dll -> No file
ContextMenuHandlers3: [00asw] -> {472083B0-C522-11CF-8763-00608CC02F24} => C:\Program Files\Avast Software\Avast\ashShell.dll -> No file
ContextMenuHandlers6: [avast] -> {472083B0-C522-11CF-8763-00608CC02F24} => C:\Program Files\Avast Software\Avast\ashShell.dll -> No file
EmptyTemp:
End::

3- Once the script is copied, click on Fix, FRST will automatically take the script from the clipboard.



Let the fix process complete; once it's done, you will be prompted to restart your PC; do so as soon as you are requested, see below.
Once your computer is restarted:
4- You will have a Fixlog file on your desktop; then send these reports to https://www.cjoint.com/ see this tutorial then provide the link generated by Cjoint in your next message.

5- CHECK AND TELL ME IF IT'S BETTER.

The fixlog is good.

Do you see this window when starting the PC? Or when you launch PowerShell?

You can install the latest version of PowerShell https://www.microsoft.com/fr-fr/p/powershell/9mz1snwt0n5d#activetab=pivot:overviewtab

Right-click on the start button (at the bottom left), then click on task manager. In the startup tab, select powershell and click on disable. Also see this page.

Fais une nouvelle analyse FRST mais cette fois avec la case registre décochée :

You must have enabled PowerShell at startup on the PC, this has nothing to do with an infection. Open the PowerShell you just installed; at the top of the PowerShell window, you will see a message asking you to set this new PowerShell as default. Click on it, and in the window that appears, uncheck the box that launches PowerShell at startup. Set the new PowerShell via the dropdown lists.

I don't understand why opening a webpage takes so long

I explained it to you here.
Insufficient RAM and a very weak processor, so it can't be otherwise.

If the internet is slow, you can test your connection here https://www.speedtest.net/fr

Your flow is very good.

You can check if the hard drive is good.
1- Test your hard drive with CrystalDiskInfo use the following color codes to interpret the results: