Upgraded to Monterey, Mac mini keeps restarting wont get to os. Only recovery mode working…bash?

Perhaps an intermediate slightly higher version of macOS would need

installed, in order to get the latest one on-board? ~ Try to go to Mojave

or Catalina; maybe Big Sur, from High Sierra.

Get download/upgrades, here:

• How to get old versions of macOS - Apple Support

//support.apple.com/en-us/HT211683

(Also note these later macOS' versions prefer an SSD & other

later hardware; plus significant details, in how they get there.)

Any later backups would only be useful to attempt a reversion to older OS.

After few upgrades in time, those won't suffice. This can mean Time Machine

& its backups are also limited, after a certain phase. You'd need a newer drive

to backup to; and consider the APFS format; if going from bottom to top.

There are things such as firmware, but those might not be consequential.

My Macs are old/older. Mojave is newest, in MB/Pro; where Catalina can be.

~ Other hardware is also limited by vintage; while I've offline considerations.

Would suggest much like previous suggestion.

A more prudent approach is suggested.

Move up to maybe Catalina first.

That is where under-the-hood changes start to take place in macOS versions.

The change is, Apple now has the Operating System housed in a Read Only Volume ( not partition ) and your user Data is housed in a Data Volume. The OS sees and presents to the User ( you ) as still one Drive.

Further changes evolved in Big Sur and again in Monterey where to Read Only Volume is not a Sealed and Read Only Volume

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

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 require an update or upGrades to 64 Bit Version