iMac Big Sur fails on install. Works in safe mode. How to identify and fix startup software issues from here?

Download and run EtreCheck. Use the share report button to copy the report and then paste it into the additional text area in a reply, here

I don’t see anything on that report that would prevent the Mac from booting normally.

But…

It’s the 8 GB iMac 21.5” HDD configuration. That’s always going to be slow, and the best bad option is installing on and booting from an external Thunderbolt SSD or USB 3.x (not USB 2.0!) SSD.

In general, the bottom-end Mac models don’t tend to last as long (usefully) as do the mid- or upper-range models, and—for various others around here posting about this iMac model—this iMac model ran out of performance with Big Sur.

The SSD will usually extend the useful life of this configuration, pending replacement with a newer model.

Google apps tend to be resource-intensice, doing who-knows-what in the background.

On the off chance that there’s a hardware problem arising here—such as a failing hard disk drive—do you have current and complete backups?

devobavishi wrote:

So how do I revert back to previous version? How can I find and delete Apps on the this machine while in safemode, before reverting back. I can not locate the apps to remove them. Safe mode shows standard apps for iOS.

I have backup for documents from this computer in icloud. Really need to get back to work, I don’t have time to mess with this. Frustrating.

Thank you for looking into this.

 A Time Machine Backup  is very useful and can be used to Revert to Previous Working macOS. But without this in place - not so simple without doing a Wipe and Reinstall of previous OS

I don't see anything, either.

Working in Safe Mode but not normally usually indicates you have third-party kernel extensions that are causing problems.

However, Etrecheck does not list any.

Apps can bundle kernel extensions into the App, and I'm not sure if Etrecheck can see those if they are not loaded (which they won't be in Safe Mode).

Another test: boot Recovery, and re-install Big Sur atop the current Big Sur install. I’ve had that clear a few weird cases.

Downgrading in general and particularly downgrading in the absence of a pre-upgrade backup is a mess, at best.