Imac 27-inch 2019 keeps rebooting

Did the problem start after upgrading the RAM?

If so, then you could have a partially seated, a bad or incompatible RAM modules.

Try reinstalling only the factory modules in their original slots. Make sure that the module are full seated in the slots and test.

What RAM modules did you use for the upgrade?

Mac are very picky. Double check the spec’s of aftermarket RAM, then reinstall it in the empty slots and re-test.

If acts up after installing the aftermarket RAM modules. Then return those RAM module and buy RAM modules from either OWC macsales.com or Crucial.com

The "Machine Check" error in the Kernel Panic indicates a hardware issue of some sort. Make sure to disconnect all external devices in case one of them is causing a problem.

You still did not answer the question of the make & model of the memory you removed before installing the Corsair memory. This is a very important detail.

I would remove the new Corsair memory and install one of the old memory modules to see how it work. If you still have issues, then remove that module and try the other older module. Also try installing a single stick in a different memory slot to make sure the slot is not bad. FYI, it is unlikely for two memory modules to fail at the same time.

Since this Corsair memory seems to be branded for Apple, it may be Ok. I have no personal experience with it since our organization usually uses Crucial or possibly OWC at times.

Try running the Apple Diagnostics to see if any hardware issues are detected. Unfortunately the diagnostics rarely detect problems, but if it does...at least you know there is a hardware problem.

You can try running Memtest86 to check for memory issues. If the default settings don't find a problem, then modify Memtest86's CPU option to "Round Robin" or "Sequential" to see if it errors or perhaps even freezes.

The Samsung SSD may also be a potential issue since the EVO series especially seems to be more problematic with Macs. You may want to test the iMac by installing macOS to an external USB3 SSD and booting externally to see if you still have the problem. It isn't a perfect test, but if this works, then it may point to a issue with the internal Samsung SSD.

You should install EtreCheck and post the report. Allow Full Disk Access.

https://etrecheck.com/

Use the Additional Text icon to paste in the report.

It may provide some insight.

I really suspect a bad Logic Board (it was my first instinct). In that case, trying the firmware "Revive" or "Restore" operation is probably the only thing left to try before having the iMac repaired. I don't expect this to do anything either, but it cannot hurt either.

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

Making the Memtest86 USB stick should take less than a minute since it only has about 15 MBs of data. Most times the USB stick is at fault since the quality of USB sticks is extremely poor. It is possible to make a FAT32 partition on the USB stick and copy & paste all the files from the mounted Memtest86 .img file to the FAT32 partition....this should also work.

At this point, I would consider reinstalling the original Apple SSD and re-testing the iMac.

Then if that fixes the problem, I would consider testing an OWC Aura Pro X2.

https://eshop.macsales.com/shop/ssd/owc/imac-27-inch/2013-2019

owc aura pro x2 ssd for 2019 iMac 

As for the EVO's, I would return if possible or put them in Thunderbolt Enclosures.

https://eshop.macsales.com/shop/envoy-express/thunderbolt-3

thunderbolt ssd enclosure for mac

This is a side issue but easy to address for your aftermarket SSD:

disk1 - Samsung SSD 870 EVO 1TB 1.00 TB (Solid State - TRIM: No)

Internal SATA 6 Gigabit Serial ATA

I've found in my own experience and from posts here that with TRIMforce disabled, SATA solid-state drives can start to slow with time. For me it manifested as the Write speeds dropping to half (under 250MB/sec) and continuing to fall as bad as 60MB/sec. OWC made the drive I was using and always said enabling TRIM was not necessary. Still, just over three years after the SSD install, its write speeds started the downhill trajectory.

With the counsel of ASC's amazing Grant Benet-Alder I was able to find that TRIM does matter. This OWC article tells how to enable TRIMforce:

https://eshop.macsales.com/blog/31619-how-to-execute-trimforce-command-with-your-owc-ssd/

I did that. You need to do several safe mode boots to fully restore lost performance. Grant suggested letting the computer "soak" in safe mode for a couple of hours. I did so several time and eventful the write speeds were restored to the ~500MB/sec expected and have stayed there.

What RAM did you have in the Mac originally when the crashes started? Just Apple or some 3rd party? If it was 3rd party the next paragraph would apply.

We've found here from hundreds of posts that the only 3rd party RAM that is guaranteed to work with the Mac model it's designed for is from Crucial.com and OWC (MacSales.com).