iMac 27 inch slow after installing OS 10.13.6

First of two replies.

Do I have a Rescue Plan In-Place. This comprises having 3 Backups using 2 methods and 1 Off Site incase of Theft, Loss or Natural Disasters. A Time Machine Backup  is very useful and can be used to Revert to Previous Working macOS. For addition purposes - two Tested Bootable Clones each to separate external drives. This is insurance incase the upgrades goes sideways. At least one Tested Clone and / or Time Machine Backup should be Off - Site

Working on the second - a little time place :-))

Part 2 of 2

Understand - this method will Wipe the Entire Drive of everything and it an not be retrieved

1 - How to create a bootable installer for macOS - it will require an external drive of about 16 GB and nothing on the drive as it will be formatted by the Apple Command used to create the Bootable Installer of High Sierra.

2 - Shutdown computer and disconnect all external drive Except the newly created Bootable Installer.

3 - Restart and immediately hold the OPTION key until the Startup Manager appears and choose the USB Drive.

4 - It will present options >> Disk Utilities >> View >> View ALL attached Drives. Choose the Upper Most Drive ( not the volumes indented and list below ).

5 - The drive normally is called Apple Media of Apple SSD - that is the drive to Erase and format as APFS with the GUID Partition Map.

6 - Once that is done >> backup out of Disk Utilities and choose install macOS.

7 - Follow the prompts and it may automatically reboot several time.

8 - Upon a final reboot - Setup Assist will present with the version of macOS High Sierra

P. Phillips

The last Security Update for High Sierra was November 2020 << is this the update in question ?

Suggest downloading the Application Etrecheck directly from a Trusted Developer and well Respected ASC Contributor. The application is free or paid from added features. Run the application with Full Disc Access ( Security & Privacy - Full Disc Access ). It will take a Snap Shot -  both the hardware and software. The Report will Not Reveal Any Personal Information. Post back the Full Report - copy and paste - using the Additional Text Icon ( 3rd Icon to last )

We can have a look at the report for possible issues and may have possible suggestions to resolve the issues.

Any Third Party Applications that will interfere with the normal operation of the OS, alter, modify, remove or delete or attempt to do so is an invitation for disaster and may require a Reinstallation of the OS.

Thank you for the Report and looking over it. Question for you, it looks like the computer OS is being run off and external SSD ?

 Adware - Adware detected.

32-bit Apps - This computer has 32-bits apps will not work on current versions of the operating system.

Samsung SSD 850 EVO 500GB 500.11 GB (Solid State - TRIM: No)

File /etc/sudoers size: Found 1624 B but expected 1563 B

Antivirus software: Apple and McAfee - Remove as per Developers Instructions.There are no known Viruses in the wild that self replicate and affect macOS. There are Malware and Adware that does affect macOS and are often times downloaded as part of an Application from Third Party UnTrusted Site and get installed along with the Application.

Launchd: /Library/LaunchAgents/macsearch.plist

        Reason: Adware name match

        Executable: /Library/Application Support/Agent/macsearch DistributerName ChannelId DeviceId Country BarcodeId Date

Launchd: /Library/LaunchDaemons/org.virtualbox.startup.plist

        Executable: /Library/Application Support/VirtualBox/LaunchDaemons/VirtualBoxStartup.sh restart

Wireshark - is it really required ?

running app: /Users/gebruiker/Library/UpdateMac/youngness/youngness ?? do not know this one

    Running app: /Users/gebruiker/Library/endocritic/TqFQjYbB/BrAKErDv/zxfnSLCo/LBGqSyyj/pristine_saxifrage - ?? do not know this one

Plug-Ins/Silverlight.plugin Remove it is outdated and not required

67 32-bit apps

Kernel Extensions:

    /Applications/Aimersoft Video Converter Ultimate.app

        [Loaded] SystemAudioRecorder.kext - com.Perfect.Driver.SystemAudioRecorder (1.1.0 - SDK 10.6)

    /Library/Application Support/VirtualBox - Would need a more robust computer and double the RAM

        [Loaded] VBoxDrv.kext - org.virtualbox.kext.VBoxDrv (Oracle America, Inc., 6.1.4)

        [Loaded] VBoxNetAdp.kext - org.virtualbox.kext.VBoxNetAdp (Oracle America, Inc., 6.1.4)

        [Loaded] VBoxNetFlt.kext - org.virtualbox.kext.VBoxNetFlt (Oracle America, Inc., 6.1.4)

        [Loaded] VBoxUSB.kext - org.virtualbox.kext.VBoxUSB (Oracle America, Inc., 6.1.4)

Suggest downloading from a Trusted Developer and Respected ASC Contributor the application Malwarebytes for Mac. It is free or paid for added features. Run the Application and it should remove the malware / adware. Once done, restart computer and test.

There are no known Viruses in the wild that self replicate and affect macOS. There are Malware and Adware that does affect macOS and are often times downloaded as part of an Application from Third Party UnTrusted Site and get installed along with the Application.

From Toronto, Ontario, Canada

Excellent work getting the Beast up and working again. :-))

Yes, obsolete is only a term used for unsupported Hardware for Parts from Apple.

May explore from Samsung specifically if TRIM is supported on this specific drive or if the Drive is already using the builtin TRIM when Samsung manufactured the unit.

Aside from that - the Report looks good for a computer of this age.

Thank you for getting back on the progress on this project.

Stay safe and well.

One more piece of information regarding Fusion Drives and if applicable to this machine needs to be made know.

How to fix a split Fusion Drive

Welcome and yes digest all. Should there be additional questions, please ask before attempting.

We share a first name only in French

P. Phillips

Understood and hope safe after the flooding.