They don't own the content according to the TOS, they get a license to use it (the Creative Commons Attribution-ShareAlike 4.0 license). They could still use it for AI training, but the model would have to be CC BY-SA 4.0 (not that AI companies care).
This definitely forbids the "I will not transfer it to others without permission from Stack Overflow" checkbox, as the CC BY-SA 4.0 license says "You may not apply legal terms or technological measures that legally restrict others from doing anything the license permits."
This definitely forbids the "I will not transfer it to others without permission from Stack Overflow" checkbox, as the CC BY-SA 4.0 license says "You may not apply legal terms or technological measures that legally restrict others from doing anything the license permits."