Upgrading to Monterey broke my Fusion Drive, any way to fix it and get data back?

Not sure this will work on Monterey but nothing ventured nothing gained.

How to fix a split Fusion Drive

After the fact & only for informational purposes

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

macOS Mojave 10.14 hardware requirements

macOS High Sierra 10.13 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, which appears to be the case for this computer

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

Tips Big Sir Upgrade Released Nov 2020

Tips Monterey Upgrade  Released Oct 25, 2021

Make Time Machine Backup  is very useful and can be used to Revert to Previous Working macOS

Notation - Mojave is the Last version to support 32 bit applications / extensions and Drivers. Catalina, Big Sur & Monterey supports only 64 bit and there is no workaround.

Suggest using Go64 to find 32 bit application before attempting the upGrade. Some or many of the Application already installed may required update or upGrades to 64 Bit Versions.

Apple warns Mac users that 32-bit app support is ending

Apple to Phase Out 32-Bit Mac Apps Starting in January 2018

https://techcrunch.com/2018/04/11/apple-starting-to-alert-users-that-it-will-end-32-bit-app-support/

Heads up regarding replacing the Internal Drive.

There appears, at the moment, there is no workaround.

Point # 1 - Does the >>  Computer Qualify for the Monterey upgrade 

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.

You are welcome.

Do come back to the Apple Support Communities ( ASC )  in the future, if / or when additional Technical questions may arise

There has been enough advise / suggestions offered for the User to make an informed and educated choice what the next course of action is required.

The suggestions have been put forth on a volunteer basis, in good faith and in the best interests of the computer.

Anything more regarding " Professional Version would be nice ".

To be effective and constructive, it should be directed to Apple Feedback

It seems you are not able to use a computer without training wheels.

You'd be better off following the guidance of an IT staff.