I'm nowhere as fanatical about it since when it's come to corporations there is no black and white, but there at least few cases I can recall:
* Even decade ago they did a lot of shady stuff when they initially separated GeForce and Quadro series. There was time when you can make little hardware mod on Geforce product that make driver think you have Quadro and magically a FP64 become twice faster and CAD application performance was doubled and tripled.
* Their OpenGL implementation was ever non-standard and allowed both code and shaders to work in situation where it's clearly should not. As result games and apps that was debugged on Nvidia hardware would never work on more conformant Intel / AMD drivers.
* In terms of Nouveau back in 2014 Nvidia started to require signed firmware files [0]. They promised shortly after to provide Nouveau with the files with clear licensing, but it took years. When files were finally released everything related to power management was missing and still not released until this day. So Nouveau can't implement recloking. On top of that they intentionally obfuscate the way firmware files stored within driver binary and also make GPU load firmware via DMA to make extraction much harder.
* Sabotaging of OpenCL in general by not implementing spec for years and keeping it generally much slower that it's supposed to be.
* Several years ago Nvidia twice added checks to their Windows drivers to stop consumer GPU drivers to work when passed into virtual machines. Both bypassed by hiding KVM identifier and changing HyperV hv_vendor_id, but it's was annoying [1].
* Nvidia forbidden to use consumer hardware drivers in datacenters [2]
* Nvidia tried to push some crazy anti competitive program to make exclusive deals with GPU vendors so they can't sell AMD GPUs in any kind of "gaming" product lines [3]
Again it's not like AMD is perfect, but that's a lot of shady stuff and I likely not even listed half of it.
[0] https://hardware.slashdot.org/story/14/09/27/1254219/nvidia-...
[1] http://vfio.blogspot.com/2014/08/vfiovga-faq.html
[2] https://news.ycombinator.com/item?id=16002068
[3] https://news.ycombinator.com/item?id=16675557