Stuck on Monterey install

Suggest restarting in Safe Mode. This will perform a Disk Repair, clear cache files and only load Apple Software, extensions and fonts.

The boot up will be slow and can take some time - Normal.

This may or may not allow the UpGrade process to complete.

I am in a similar situation as @tomcatch. I have downloaded and installed Monterey from the software update window (I have a late 2015 iMac running Mojave). All was well until the installation stalled at the apple screen.

This happened after a couple of hours. I powered off, restarted in recovery mode, run a Disk Repair, and restarted the upgrade. Until the system allowed I was even following the install log and all seemed well. Now I am again stuck at the same point.

Am I just impatient and need to wait hours for this to complete?

The apple page How to upgrade to macOS Monterey - Apple Support does say "It might be easier to begin in the evening so that installation can complete overnight." Does this mean that it can take many hours to complete?

A colleague upgraded his desktop from High Sierra (!) to Monterey and it took him 1 hour!

I am worried.

The Age of this computer will Govern what newer version of macOS it will Qualify to install. Use About this Mac from the Apple Icon on Desktop - the required Information will be there.

With the above information in-hand - follow this How to get old versions of macOS and verify what version this computer Qualifies to install.  For Best results use Safari to commence the download as Others may not work.

Safari will open a redirect and open the Apple Store where the download can commence.

Computer Qualify for the Monterey upgrade

macOS Big Sur 11 hardware requirements

macOS Catalina 10.15 hardware requirements

Caution - jumping over all the newer versions and directly to Big Sur  / Monterey on Qualifying computers is Technically possible - there are those who have attempted and were successful. Then there are those who attempted and had less than good results.

If this is a Production or Mission Critical Set-up - a more prudent and measure approach is suggested. 

The above is from observations on the Apple Support Community Forums and IMHO

Upgrading from Mojave what version and was Mojave Fully Up To Date with all security Updates applied ?

Is there a Fusion Drive installed. Fusion Drive were good in their day for extra storage but it appear ( from observations ) since Big Sur and again in Monterey - the OSes are really designed around all SSD configurations. Yes, it will function on Fusion Drives but with a major Hit to performance.

Depending on many factors

1 - is FileVault Enabled

2 - If yes, had it finished Decrypting the drive Before the Installation of Monterey commenced.

3 - Empty Disk Space If upgrading from macOS Sierra or later, your Mac needs 26GB of available storage to upgrade. If upgrading from an earlier release, your Mac needs up to 44GB of available storage. 

4 - Drive format when Mojave was used. Was the drive using the APFS format or Still using the Older HFS Journaled format.

5 - Was there any Antivirus Software installed in Mojave. If so, that too can badly interfere with the upgrade and in some cases have seen a total failure of the upGrade.

6 - There are reports appearing on the ASC Forums regarding failed installation of Monterey on older Qualifying Apple Computers. In most cases this is related to having a NON Apple Original internal drive ?  

The EFI Boot ROM included in Monterey is verifying for Original Apple Drive and if not found , may Balk or fail to upgrade to Monterey. 

Reports indicate the EFI BOOT ROM is Required to Flash the Computer and is a  requirement for a Successful Monterey Installation

Any one or combination of the above can or may come into play with just how long the process will take.

After the download is completed the automatic installation typically can take up to an hour for Monterey, more or less with multiple automatic restarts. You likely have a corrupted downloaded file and it cannot complete the installation. Did you use Wi-Fi for the download? If so, it is too slow for these very large files and almost always fails. Instead, use a wired Ethernet cable for this download and do a new download.

This computer DOES qualify for the upgrade! I did it from the software upgrade window which redirects to the Apple Store.

I have done many upgrades and the upgrade tells you immediately if the computer is not compatible. It does not hang.

My question is: if apple suggests to do it overnight, does it mean that it *might* take several hours?