This goal of this post is to centralize all known information on using Dell systems with Apple Thunderbolt Displays.

People have been forced to jump through hoops to get these devices to work with Dell thunderbolt controllers for quite some time now, and as of January 21st, 2021 they killed the compatibility on multiple models with a Firmware update named Intel_TBT3_FW_UPDATE_NVM46_PHY71_A02_4.46.152.001.exe which completely disables these displays. There's nothing wrong with the monitor, Dell's firmware just won't authorize it.

We're a small market, but we are dedicated. We also happen to be engineers, artists, producers and very creative when it comes to problems.

Because it's a Thunderbolt firmware update this includes Dell AND Intel, as Intel is the real author of the Thunderbolt firmware code, and these updates are tied with IMEI and microcode updates. This makes it a difficult issue to resolve. With a sample size this small, getting either party to care or even post a support page has been impossible until 3/18/21 when Advanced Resolution Services finally got back with me for a real dialog, which was greatly appreciated after banging my head against a wall for weeks.

The first real issues became evident with Intel's 10th Gen based NUCs, and Intel has declined to support those units at this time.
https://community.intel.com/t5/Intel-NUCs/Apple-Thunderbolt-Display-27-DOESNT-work-with-NUC-gen-10/td-p/1204298

Warning:
Unfortunately there have been multiple reported incidents of Support Assistant automatically applying these updates without user input as it did in the past.

Downgrading: Manually downgrading is unsuccessful at this time. I've played with the binary for the NVM and I can't force it to write using any of the tools I have. I have been unable to find a functional override in the previous version using Dell's older firmware updaters.

For Thunderbolt controllers that have not been updated to firmware 46:

Configuration that was working:
Apple Thunderbolt Display -> Thunderbolt 3 (USB-C) to Thunderbolt 2 Adapter -> Dell Device
Apple Thunderbolt Display -> StarTech TBT3TBTADAP Thunderbolt 3 to Thunderbolt 2 Adapter -> Dell Device

BIOS Setup:Page 1
- Enable Thunderbolt Technology Support
- Select Security Level - No Security
Page 2
- Select BIOS-Assisted Enumeration

For Thunderbolt controllers that have not been updated to firmware 46:
Do not update your thunderbolt controller at this time. Disable Support Assistant and related service.

Resolution:
Unknown at this time. Dell claims to be looking into it. Intel has declined to assist their own customers.

Lastly, why am I involved? I had written Dell off after they refused to honor the full duration of the warranty on my last gaming laptop and figured I'd ignore them forever. I made the mistake of reinstalling Windows and installing the newest version of Support Assistant to grab the drivers, and this proceeded to gather up all 4 new updates and run them without review or approval. There are multiple reports on the forums about SU running without input, but we're being written off as liars.