IANAL

> Someone reverse engineered the plug-in and put it into orca slicer and then claimed that the plugin should have been GPLed to begin with which I find dubious. I don't really see it being much different than downloading closed drivers on Ubuntu but I'm also not a open source lawyer.

The GPLv3 specifically was written to address a problem called "TiVo-ization", which is when a hardware vendor uses some trick (DRM, proprietary blobs, whatever) to prevent users from actually running modified versions of the software.

The AGPL, the license of this particular software, extends the GPLv3 with protections for users of network services:

> Simply put, the AGPLv3 is effectively the GPLv3, but with an additional licensing term that ensures that users who interact over a network with modified versions of the program can receive the source code for that program. In both licenses, sections four through six provide the terms that give users the right to receive the source code of a program.

https://www.fsf.org/bulletin/2021/fall/the-fundamentals-of-t...

And on TiVo-ization: https://en.wikipedia.org/wiki/Tivoization

The Linux and proprietary drivers situation is more complicated, but proprietary drivers on Linux are generally restricted to interfaces that Linux chooses to expose to them for that purpose. But the Linux kernel seems to take a narrower view of what constitutes a derivative work than was likely intended by the FSF in writing the GPL. Under a "traditional" reading of the GPL, those proprietary drivers are meant to be illegal. Whether some or all of the linking done by proprietary drivers in the Linux kernel is really allowed by the GPL or not is somewhat untested, I think.