Since a month ago, before the blackout, he build kbin by himself
Per that link you gave, ernest started building kbin in January 2021, launched the first instance in September 2021 and started to work on kbin full-time in the end of 2023 (EDIT: 2022, of course; always refreshingly embarrassing to make mistakes when correcting others). Not directly mentioned in that link, but hinted by the graph there, the kbin.social instance launched in April, now close to three months ago.