Big Sur Update 11.6.1 fails to install on iMac

Went to website, received two error messages: "You do not have permission to run this application. Contact your computer or network administrator. (I'm the computer administrator!) and "Safari cannot open this file. No application available."

Would download from App Store work?

Thank you for the prompt and detailed response. I take full responsibility for getting everything screwed up by carefully following my Verizon Network Manager son's hands-on updates since High Sierra!! This explains the long list of unresolved problems I've had which he kindly ascribed to Apple to include problems with FileVault, inability to get Time Machine to work and adding CleanMyMac, first Malwarebytes, then Kaspersky Internet Suite among others. I will follow Step 1 at the earliest opportunity. Do I need to take any actions while in Safe Mode after uninstalling CMM and before restarting normally?

Wanted to add a few points re this computer been a mess while you are reviewing latest EtreCheckPro report:

Advised by son not to allow auto install of updates as updates often buggy. Wait till cleared by Tidbits, MacRumors or other Mac publications then update manually.

First major problems with son update to Mojave; son advised need to encrypt hard drive via FileVault which he did. Seemed to take quite a while but 2 days later (after he was gone!) crashed and asked to de-encrypt, which I did. Seemed to go very fast but after then Time Machine no longer worked. Instead of backing up the 450GB on the drive as usual continued to back up almost to 3 TB which is size of whole hard drive. I stopped the Time Machine backup after before 3TB. Son couldn't offer resolution so added Carbon Copy Cloner which seemed to work but admit I never really tried to reboot to the CCC copy before son updated iMac to Big Sur (without another backup!)

Have frequent beach balling with Notes app which sometimes resolves, sometimes needs Force Quit.

Son advised I should add ClamXAV to Kaspersky as he suspected compromise of Apple Mail but again no additional details . I did not follow that recommendation, but insisted I continue to use use Kaspersky as Apple macOS more and more under attack?

Thanks for the follow-up. No, my son has totally been an Apple guy from the beginning, getting personally or through his company the latest iMac Pro, MacBook Pro, iPhone, Watch, AirPod Pro etc as soon as available. He chuckles over my 12 year old Win7 laptop that still works with over 70GB of iTunes music on it. Despite the frequent problems, really hate to be unduly critical as he has given me the only Apple products he doesn't use, two 12.9" iPad Pros (First Generation with 128GB and Last with 1TB storage.)

When you wrote "Okay there is one major issue I see that could be cause..." did you mean inability to get Time Machine to work on three different 2TB+external drives or the two security settings disabled? My son had advised me on the latter for the reason described in previous post but when I went in to System Preferences and turned them back on, multiple updates were immediately installed including Big Sur 11.6.1 and the latest Device and Safari updates!

I actually have two backups, Carbon Copy Cloner V5 and Acronis 2021 which were updated just before the upgrade to Big Sur but never tested. Just can't get the Time Machine backup to work as described in previous post.

I am more concerned now that multiple apps I deleted either 10 months ago (Malwarebytes on advice of Kaspersky) or recently with CleanMyMac and Kaspersky (CCleaner, MS Onedrive, 2 ProtectStar apps, etc) still show as installed on the second report I sent. Also the report stated 11 32bit apps installed when Go64 alleged 299 apps (mostly Apple) were 64bit but only one DVD Cloner 2019 was still 32bit and then only the EjectDisc component.

Finally the report recommended turning off Printer and Screen Sharing. I turned off the former but wonder if I need the latter to connect with the two iPad Pros which are the only devices I use beside the iMac. Can turn Screen Sharing off if that is a major security threat. I use an xFinity WiFi Gateway.

Sorry for the information overload but you are clearly the first (post several Apple Support calls) who has more answers than questions. Mea culpa.

By Erase and Install, you mean wipe the drive clean and reinstall all the apps without the benefit of a backup? I do have Carbon Copy Cloner and Acronis backups from Mojave but I have read Apple no longer provides Security Updates for Mojave. Also I do have a lot of Notes, Books, and Photos (hundreds of GB) I would hate to lose considering I have been adding them without a clean install since I bought the iMac in January 2016.

I tried once again to set up the two Seagate Backup Plus units, one 3TB one 5TB I have for Time Machine by reformatting for Big Sur (previously used under Mojave) but when I tried to reformat to AFPS, the erase was cancelled stating the drive could not be unmounted because it is in use by process 79 (Fsevendtsd). Couldn't unmount drive: (-69888).

If Erase and Install is the only option, could some of the files mentioned be copied to an external drive using Finder, assuming I could reformat one of the existing drives or a new one as you recommended to AFPS? Also it seems the E and I option wants you to use Monterey instead of reinstalling Big Sur.

Do you have time/interest to address any of the other subjects in last email? Also my son recommended I review some of the many blog entries/articles from sources like MacRumors, MacIntouch, and Michael Tsai before I totally accept the infallibility of Apple updates and upgrades and the danger of using Third Party apps on my iMac.. Caught between two Experts?