trying to load ventura from monterrey "your computer restared because of a problem. press any key or wait a few seconds to continue starting up"

Try the following:

#1 - boot into Safe Mode according to Start up your Mac in safe mode - Apple Support.

NOTE: Safe Mode boot can take up to 3-5 minutes as it's doing the following; 

• Verifies your startup disk and attempts to repair directory issues, if needed

• Loads only required kernel extensions (prevents 3rd party kernel/extensions from loading)

• Prevents Startup Items and Login Items from opening automatically

• Disables user-installed fonts 

• Deletes font caches, kernel cache, and other system cache files

#2 - go to the System/Software Update preference pane and begin the download.

#3 - run the installer from the Safe Mode.

ecouv wrote:

Trying to load Ventura from Monterrey. Over the last few days I’ve updated sequentially from Catalina to Big Sur to Monterrey with no problems. Now it keeps cycling back to the white progress bar after a message in several languages saying "your computer restarted because of a problem. press any key or wait a few seconds to continue starting up"

I believe this is the correct info but I can’t access About My Mac.

Early 2019 iMac 27”

32 gb RAM

Not sure what RAM has to do with it...(?)

Verify you have adequate free storage space.

Uninstall all third party apps that are Cleaners/Optimizers/VPN/Anti-Virus

all known to cause issues on the macOS

ref: How to upgrade to macOS Ventura - Apple Support

You can always try form a SafeBoot—How to use safe mode on your Mac - Apple Support

login and try again.

if necessary— Revive or restore an Intel-based Mac using Apple Configurator - Apple Support

If you are having WiFi issues try power cycling your router.

Otherwise use an Ethernet Cable to connect your iMac directly to the router to avoid any hard to troubleshoot WiFi issues.

Make sure to disconnect all external devices in case one of them is causing a problem.

It sounds like the iMac is having Kernel Panics. This can be caused by third party software although Safe Mode should be able to temporarily bypass the third party software, or the iMac has a hardware issue. Try running the Apple Diagnostics to see if any hardware issues are detected (very rarely detects any problems).

Do you have a good backup of this system? If not, it may be tricky trying to get a backup now, but you should try.

If you have a good backup, then you can try a "Restore" firmware option which resets the T2 security chip & firmware. Afterwards you will need to boot into Internet Recovery Mode (Command + Option + R) in order to reinstall macOS. FYI, the "Restore" destroys all data on the internal SSD and should properly prepare the SSD for macOS to be reinstalled. Sometimes this is the only way to recover. You can try the "Revive" feature which theoretically should not affect the current data on the internal SSD, but I have rarely seen the "Revive" fix anything. Unfortunately this process does require access to another Mac running macOS 12.4+ (at least the last time I checked....unfortunately Apple keeps increasing the OS requirement of the host Mac believing everyone has access to two very recent Macs).

Try Option Booting to see whether any bootable volumes appear on the Apple boot picker menu. Maybe you will see more than one boot option. To Option Boot you need to hold down the Option key immediately after hearing the Startup Chime.

If your ISP/router issues are resolved, see if you can boot into Internet Recovery Mode using Command + Option + R to access the online Ventura installer. If so, then you can maybe check that the drive layout looks Ok and run First Aid on the hidden Container. You can also see whether you can select the previously working APFS system snapshot for booting or restoring. I don't know if this is still possible, but if an OS update/upgrade went wrong it was possible to boot into the installer and select "Restore from Time Machine". Then select "Local Snapshots" to see whether there is a local macOS system snapshot available (one should have been created during the OS upgrade process). If one exists you should be able to select it so once rebooted it will hopefully be booting from the last known working version of macOS.