In the past, I have tried deleting my LinkedIn account several times. Every single time, in the last step, the final deletion button was inactive, and no reason given for why it's so. The Internet wasn't helping my either.

So today, I tried once again: But this time, I used my browser inspector, removed 'disabled="true"' for the "Done" button, then clicked it.

voilà! LinkedIn said: "We’ve closed your account."