This is the emails between the YouTuber YGK3D and Anycubic, it seems like they won’t send 3D printers to reviewers who mention their GPL3 license violations.
tl;dr Anycubic uses open-source software for their firmware, but doesn’t make it public as per license agreement, and they don’t seem to be friendly to anyone who calls this out.
More info: https://www.youtube.com/post/UgkxIMpZTkXqFo0H6pDwhZpdYqMYvLhPvWA5?lc=UgxA-4LYvwrnonXuXsZ4AaABAg
They did (do?) have the tab you have to break to flash new firmware to your printer though.
It’s a warranty & legal thing. Prusa had users flash unsupported firmwares, break their electronics with bad configs and then claim warranty on them, and there are also ones available that have safety features tweaked or disabled that could end up with a fire.
You are still free to do it, the tab just a permanent way of clicking “I understand doing this voids the warranty and I’m going it on my own risk” - which you’ve basically always been agreeing to modifying the firmware anyway.
I have Prusa Mini+ and it still lets you flash unsigned firmware, you just need to enable it. Also PrusaSlicer is the best imo.