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
There is also Prusa, which doesn’t lock down their printers for meme sake.
They did (do?) have the tab you have to break to flash new firmware to your printer though.
I have Prusa Mini+ and it still lets you flash unsigned firmware, you just need to enable it. Also PrusaSlicer is the best imo.