External HDD stuck "loading". Help, all 3 backup drives failed at same time!!

There is no good way of really testing the laptop other than try connecting known good items directly to each of the laptop's USB-C ports. You should even rotate the USB-C connector 180 degrees upside down as well when testing each port as that may reveal whether a particular USB-C port is half bad. If you find known good devices don't work on one or more of the ports, then it is likely those USB-C ports on the laptop are bad. Keep testing simple by connecting devices directly to the laptop with simple adapters if necessary (like the Apple USB-C to USB-A adapter).

I did address the issue of possible adapter, cable, and dock/enclosure issues in my previous post and suggested disconnecting all devices and connecting the drives directly to the laptop. I would have been more specific if I had more information at the time since there were (and still are) so many unknowns here. A lot of third party accessories and peripherals are pure and utter junk that barely function and doesn't usually last very long. Even good quality products don't always hold up like they should these days. You will have to purchase a new well respected brand of adapter/hub to test your devices and methodically figure out which items work and which do not. Any one of those connected devices could be bad and affect your other devices in unexpected ways. I would always start with the common item you are using to connect these drives and expand out from there if necessary. Keep things simple when testing so that you can confirm individual items are each working, then you may need to add in the other items in case there is a compatibility issue or whether you may have overloaded an adapter/hub/dock.

I agree with @steve626 that you should try the drives on another computer.

If you want to know whether each of those hard drives is still healthy, then use DriveDX as I mentioned in the other post and post the report(s) here if DriveDx can access the external drives' health information. A drive does not need to mount in order to check the drive's health. Sometimes when a well used drive sits for a long time without being used it may not always spin up or work properly.

How were these backups created? Time Machine, or did you use some third party backup software?

What size are these backup drives and have you used them with this specific Voyager dock before?

Are these backup drives hard drives or SSDs?

Have you tried disconnecting all external devices and have you connected the backup drive directly to the laptop? Is the laptop plugged into the charger?

Have you tried using another USB drive dock or enclosure or using a different USB Cable and adapter? Try connecting the drive to another USB-C port especially on the other side of the laptop. Also try rotating the USB-C connector on the drive cable 180 degrees upside down (I know this sounds crazy, but it can sometimes work if the USB-C port is bad).

Is your laptop booting and working correctly or is this the reason you need the backup to restore the laptop to a known good state? Or are you just trying to restore a few file instead of the whole system?

Are you booted into macOS normally when trying to access the backup? Have you tried booting into Safe Mode to access the backups?

If your laptop is able to boot normally or into Safe Mode, then you can attempt to check the health of the external drive(s) by running DriveDx. You will need to install a special USB driver so that DriveDx can access the external drive's health information. However, even with this special driver some USB drives will still block the necessary communication to access the USB drive's health information. Post the DriveDx reports here using the "Additional Text" icon which looks like a piece of paper.

Edit: I forgot to mention that Drive Savers and Ontrack are to professional data recovery services that are recommended by Apple and other OEMs plus both vendors provide free estimates. Our organization used Drive Savers several times many many years ago and we were satisfied with them.

I am concerned that the common factor to all three drives is your laptop. If each drive has a 5% chance of failure (I think the probability is actually lower than that), then two failing is 0.25%, and three is 0.01% and given that these drives typically last at least 3-5 years (often longer), the likelihood of all three failing AT ONCE is markedly less even. It's like you won the lottery. I seriously think something else is going on.

I think you should try the drives on another computer before trying a drive recovery service.