I am tweaking the instructions, it should be soon.

Did you send those instructions via email?  I haven't seen anything.  Same problem this morning when I booted up.  Pink flash on login, and then kernel panic with:

panic(cpu 0 caller 0xfffffe001ad81798): "dart-apciec1 (0xfffffe2333344000): DART(DART)

Unplugged the Thunderbay, rebooted, waited 2 minute, then plugged in the Thunderbay--no issues.

I think this is a text edit issue, it no longer has text files, you need to save and remove the extension. I will get .rtf added, I think. (there is some exploit risk, but not as much with .rtf they cannot contain executable scripts.)

I would rather have panic logs as txt attachments, as they make the forum unwieldly

Did you try connecting 2 minutes after startup? I think that is the temporary workaround.

Are you also willing to try to capture a core dump from macOS on one of these crashes?

I am preparing instructions

But, the problem persists.  As soon as I enter my password at login, the screen freezes, flashes pink, and reboots.  I unplugged the Thunderbay, rebooted, and it started normally.  Here's the kernel panic again, and I'm attaching an updated

tech support report:

"dart-apciec1 (0xfffffe23334c4000): DART(DART) error: SID 2 write protect exception on write with DVA 0x80074000 (TTBR 0 SEG 0x40 PTE 0x1d) ERROR_STATUS 0x82000488 TIME 0xb93bd6fe6 TTE 0x170b5052c001 AXI_ID 0)"

This looks a lot similar to the error I see in my kernel panics on the other m1/Big Sur thread. In my case it is indeed a fresh install, without any other kernel extension besides the SoftRAID kernel extension. It is also worth noting that the kernel panics happened during the release (11.3.1) version of BigSur as well as the 11.4 now. 

here are lenghty instructions, which will help you delete them all. unsigned extensions cannot load in Big Sur. and some older extensions can cause problems, such as the HP printer driver from 2013.

I also wonder if the NTFS driver is partially responsible. It has been correlated before, so lets do this test: delete all the unsigned and unknown extensions per below. then delete the HP , Dymo  and logmein drivers.

I wonder about the google driver, it is dated 1980, which can cause issues, perhaps reinstall it. But leave the NTFS driver. Restart and see if you get the panic.

If you do, then delete that driver and see if the problem goes away.

Instructions:

Open a System Profiler report (about this Mac).

Under the Software tab on the left, find and Click extensions
Now click on the "obtained from" column on the upper right.
Expand the upper window:
The middle bar pulls down, so you can view more extensions in the window and also have room below to see the information about each extension as you click on it. I would make it about half way.

Now, scroll all the way to the bottom, where you see "not signed" extensions in the Obtained from column. Every one of those must be deleted.

You also need to delete all the older signed extensions, especially printer extensions

When you click on any extension in this window, the lower half window has details. You want the location, i.e, path to the file

The "location" is the path to the extension. You can select this path and "copy" it.

the remove command in terminal is this:
sudo rm -r
Then you need to make sure there is a space after r, then paste in the path

For example, if you were deleting an extension like an HP Printer, commonly an issue, its "location" is this:
/Library/Extensions/hp_io_enabler_compound.kext

So the terminal command will be this:
sudo rm -r /Library/Extensions/hp_io_enabler_compound.kext

After you delete all the unsigned and unknown extensions, delete the 3 identified developer extensions above.

When all are deleted, then paste these two commands into terminal to reset the extensions cache:

sudo kmutil clear-staging

sudo kextcache -i /

restart and test.

Delete the NTFS driver with the same method, including the two extensions to clear the extensions cache:

sudo kmutil clear-staging

sudo kextcache -i /

panic(cpu 0 caller 0xfffffe002f8d5798): "dart-apciec1 (0xfffffe23334c4000): DART(DART) error: SID 2 write protect exception on write with DVA 0x80074000 (TTBR 0 SEG 0x40 PTE 0x1d) ERROR_STATUS 0x82000488 TIME 0xb93bd6fe6 TTE 0x170b5052c001 AXI_ID 0)"
Debugger message: panic
Memory ID: 0x6
OS release type: User
OS version: 20F5046g
Kernel version: Darwin Kernel Version 20.5.0: Thu Apr 15 05:31:18 PDT 2021; root:xnu-7195.120.38.111.1~4/RELEASE_ARM64_T8101
Fileset Kernelcache UUID: 615809CDB4F0A01AF4AB07A3C58C17BE
Kernel UUID: FD028752-4986-3772-8987-33E57D3A2F9A
iBoot version: iBoot-6723.120.33.0.1
secure boot?: YES
Paniclog version: 13

The workaround is to unplug the Thunderbay before startup, and plug it back in after the Mac is fully booted.  The kernel panic happens immediately upon login, with a brief flash of a pink screen.  Not sure it's related to SoftRAID, but I was running the Mac for a couple months waiting for the update to SoftRAID, and I never had the kernel panics during that time, even with other single drives attached to the Thunderbolt 3 port.   

Not a critical issue with my workaround, but I'm hoping this will help others and lead to a solution.  Happy to answer questions.