The GPU, not the TPM, is the root of hardware DRM

DRM implements the same problem Copyright does, but in a different place. To explain that, here's some backstory:

Copyright defines art as a good (instead of a service), and demands everyone play along. An artist can use their copyright to monopolize both the distribution and the derivation of their work. Effectively, this places a wall between any would-be collaborators, because collaboration is derivative. In a world without copyright, you could collaborate with the work of Disney by making derivative work. With copyright, however, Disney can demand you stop that work by monopolizing its copy. By abusing this demand, Disney can entrench itself as the only Mickey-Mouse compatible corporation.

In the software world, collaboration of work requires source code redistribution. Because of this, the social incompatibility that copyright is founded upon translates into literal software incompatibility; including proprietary software platforms and libraries. For example, Microsoft Office has entrenched itself as the "industry standard" for rich text and spreadsheets by leveraging the incompatibility of its data formats. While collaboration isn't impossible, Microsoft is granted a legally-enforced anticompetitive advantage from its copyright monopoly.

NVIDIA uses the copyright monopoly of its CUDA implementation to sell more hardware. It is able to do this because the hardware and software engineers are both part of the same vertically-integrated corporation. Because of copyright, AMD's software engineers are not allowed to collaborate with the CUDA developers, and AMD drivers cannot be made CUDA compatible.

This is where the story gets to DRM: Apple, Amazon, Facebook, Google, and others are all vertically integrated hardware-media-advertising corporations. Each of them wants to abuse their respective copyright monopolies (their media businesses) to sell hardware, just like NVIDIA does with CUDA. To accomplish this, they told us the exact reverse story: Digital Rights Management.

The story of Digital Rights Management says that hardware needs to be incompatible in order to enforce the copyright monopoly. See what they did there? Now any anticompetitive advantage that we get in our hardware and advertising businesses was all just from us doing whatever it takes to support those poor starving artists!

I can hear you asking yourself, "But where is the hardware incompatibility?". That's the extra sneaky bit on top. Unlike having a clear winner and a loser like NVIDIA and AMD, hardware-media-advertising corporations are all winners. Each one of them benefits from the other using DRM. All of their moats intersect into one giant ~~swamp~~, I mean lakefront development.

Here's an example to chew on: App Stores. Both Google and Apple have their own separate incompatible app stores. Sure, it's a loss to Google when a popular app only works on iOS, but that's a two way street. The important part is that they have a moat at all: when the little guys try to make a competitive alternative, they drown. There is plenty of room for two players at this game, and the intersection of moats guarantees there will never be a third. Even when Apple's moat starts to flood Android Island, what's left standing will be worth more than a drained swamp.

TEE is nice, but it's a pretty different use case all around, and the two are actually quite complementary:

TEE is effectively an execution environment below ring 0, together with some hardware isolation as you mention. But by itself, solutions based on it can't hold any trusted key material, so can't be used in attestation contexts.

TPMs and other types of secure enclaves or secure elements include secure storage and can come pre-loaded with external root of trust keys, which allows attestation (and by extension trusted computing use cases), but also completely local useful things like enforcing a PIN retry limit on usage of a hardware-stored SSH key.

But since TPMs are by design self-contained and don't have any input or output capabilities, mediating user access via a TEE and some minimal OS providing a user confirmation UI can be very powerful (for example so that malware can't lock you out of your own SSH keys by just entering the PIN incorrectly repeatedly).

In most well designed systems the only keys that are useful are held in HSMs that won't export them to anyone, so you can't easily do that. You could at best sign a few things with the keys if you were able to compromise HSM credentials, but, once you were caught your access would be revoked along with anything you signed.

That device makes no mention of stripping HDCP and I can't find any evidence it does that on the maker's website. What makes you think it will strip HDCP?

Yes, that's very common. In Windows 11 Pro (not sure about other editions) you can enable BitLocker and turn on auto unlock with no PIN. Though if someone steals the whole PC I'm not sure how effective that is. With a PIN set the TPM will enforce rate limiting to prevent brute force attacks, which should be more effective in that scenario. Most modern phones do something similar: user data is encrypted with a TPM key accessed using your lock screen code on boot-up.