2015 Macbook Pro Retina cannot update to Monterey

You can try booting into Safe Mode to see if the install will proceed. If it works, then you most likely have some third party app installed which is interfering with the normal operation of macOS.

You can also try booting into Internet Recovery Mode using Command + Option + R to access the online macOS Monterey installer. Unfortunately some Macs may only boot to the online installer for the version of macOS which originally shipped with the Mac from the factory.

Another option which I highly recommend is to create a bootable macOS USB installer by using the instructions in this Apple article:

Create a bootable installer for macOS - Apple Support

At the very least, having the bootable macOS installer will give you more options in case something else goes wrong during the upgrade process especially since Internet Recovery Mode cannot always be relied upon.

Anthonyinit wrote:

Above is the Partitions i'm having. "Library" is my 2nd partition just to keep some backup files etc...

EDIT: What is strange i have the same 13" Macbook Pro 2015 Early i had no issues installing Monterey. It has the same partitions. one is for the OS other is for backup or Library.

I hope this is not a backup of data stored on your boot drive for this laptop. Storing a backup on the exact same drive (and computer) as the original data is not a backup. If the SSD fails, then both copies of the data are gone with little to no hope of recovery from an SSD even with an expensive professional data recovery service. SSDs can fail at any time without any warning signs....even a brand new SSD.

Make sure to have frequent and regular backups of your computer and all external media (including the cloud) which contains important & unique data. Backups should be stored on dedicated external media (at least one copy anyway...the more important the data, then the more backup copies you should have with one stored at a separate physical location). Also, most cloud based apps are only for syncing data between devices and are not considered a backup. There are cloud based backup services available, but they advertise as a backup service instead of a file syncing service.

Also, in my experience it is a bad idea to use multiple partitions on any drive because people almost always realize much later that one or both of the partitions are too small. Fixing the problem is always risky and many times will require erasing the whole drive & starting over....many times resulting in data loss as well. These forums are full of posts like this.

When using an APFS file system, you can just create a new APFS volume within the same APFS Container (the Container is hidden by default). This new APFS volume sort of acts like a separate partition, but does shares the same storage pool as the other APFS volumes within that same Container. macOS already utilizes this new behavior for separating out various aspects of macOS.

Add, delete, or erase APFS volumes in Disk Utility on Mac - Apple Support

It is compatible. Try while in Safe Mode.

Use safe mode on your Mac - Apple Support

Unfortunately your last picture is missing a critical part of the image showing the volume names. You can only install macOS onto the proper volume.

Is this picture from initiating the macOS installer from within a normal boot of macOS?

Also, what is the specific reason for upgrading to Monterey now? If you are having problems with your current installation of macOS, then you may need to first resolve that issue before upgrading to a new version is possible. We are missing too many important & critical details regarding the history & methods being used here.

What is the version of macOS currently installed on this laptop?

Are you running any anti-virus apps, cleaning/optimizer apps, or third party security software? Is this laptop being managed? Check the "Security & privacy" System Preferences to see if any Profiles are listed.

Edit: Also, what is the partition type and file system format of the current boot drive? And exactly what volume are you selecting in that last photo?

Go to the Apple menu->About this Mac and tell us exactly the model and year: does it say 2015 in there?

Maybe you bought it in 2015 but it is a 2014 model? In that case it would go only up to Big Sur.

Try using Option-Command-R during startup, you might be offered the latest macOS that is compatible with your Mac.

Beyond that, I'm out of ideas.

You're welcome.

Anthonyinit wrote:

Above is the Partitions i'm having. "Library" is my 2nd partition just to keep some backup files etc...

You didn't assign the "Library" partition to Time Machine by any chance?

You're welcome. I'm out of ideas. Perhaps someone else will know.